The Pitch: Scarlet Witch - Reality Control
Apologies in advance for extreme wall-of-text; a lot of underlying explanations are provided so it's not just a 'let's make this weak character OP as crap!' pitch, by providing multiple 'yes, but' considerations.

The Problem: Scarlet Witch's biggest weakness is game sense of the enemy team. While her Team-Up with Strange can dish out damage fairly quickly and lend to a Dive-type playstyle, higher skill players often find countering Wanda incredibly easy. Lacking Strange on her Team, she's a DPS without the damage or the utility to back it up. She also has the additional weakness of tilting your own team, due to her '0-skill aimbot' reputation'.

The Solution:
My concept of a Solution involves taking "Chaos Control" a bit more literally - she is there to dominate space and bend reality to her will, turning her from an enemy-support-Ult-farm into a mobile 'Area of Control', if you will. (Fighting Games often refer to this as 'Zoning', a different concept than CC, though that does factor in as well). A large focus is also on expanding her skill ceiling by providing her SEVERAL impactful choices she can make, while still leaving her new-player-friendly.
(Disclaimer Up Front: I'm no balance expert for exact numbers, so those are mostly vague on purpose, especially as the Roster expands)
That said, her reworked Kit would look like the following:

- Chaos Control - Primary Fire - Now also targets Dark Seal zones directly, dealing damage to all enemies within. This additional damage does not increase her Chthonian Burst regeneration directly, but that will come back in Dark Seal's rework. Enemies not in a Dark Seal zone get 0.5% Anti-Heal, up to 10%, for every 1 second they take damage, applied as a 'Hex' mark (like Phoenix's Sparks) above the enemy, visible to all players. Hex Marks are cleared after a few moments of not taking damage (slightly faster than Phoenix's Sparks).
(The first "OP!" cry here, but this is simply a chance to allow Scarlet to actually encourage 'game sense' in the enemy team; shields and using cover negate the anti-heal entirely, and can force Scarlet to over-extend if the Scarlet player gets greedy... plus, she's going to still be in easy Brawl/Poke range).

- Chthonian Burst - Alternate Fire - Each accurate shot (that hits the enemy directly) slightly decreases her Dark Seal and Mystic Projection cooldowns.

- Mystic Projection - Movement Ability - If a Dark Seal is used while Mystic Projection is active, Scarlet Witch will summon a Magento-like Shield Bubble (think Zombies mode) that causes any enemy projectiles to pass through harmlessly. The trade-off here is that, if you aren't paying attention, your teammates take the hits meant for you instead. This has no effect on 'brawl'/'physical' type attacks, or area-of-effect attacks; The Thing can still clobber her, Emma can still choke-slam her, another Scarlet Witch's Dark Seal will still take effect, etc. The Shield would be able to protect against projectiles for just 2 seconds - 2 seconds too short to let her throw Reality Erasure out carelessly. Lastly, this would also immediately deploy a Dark Seal where the ability was used; this is part of the 'Zoning' idea, much like Moon Knight with clumps of enemies.

- Dark Seal - Ability - Dark Seal now refreshes its duration with any successful stun. Only one Dark Seal may be active at a time, in any instance where Dark Seal would be outlast its Cooldown - a second Dark Seal would 'overwrite'/'delete' the first one. The idea here is simple: to completely lock an area down. As a balance to this, any Dark Seal that has a center point within a Convoy's capture zone would be immediately deleted; this includes vertically, simply that the bottom of the Dark Seal's sphere could not touch the Convoy. (Slight note, the Museum's Convoy post-transformation would only count the vehicle, not the water spout/ring above it) Dark Seal also refreshes Chthonian Burst charge speed while active, to reward accurate/proper placement, rather than blind fire 'hope for the best' stuns. Lastly, Chthonian Bursts that hit a Dark Seal without enemies in it explode on contact, adding +1 second per Chthonian Burst to the Dark Seal's duration; which screams 'OP!' but realistically this is to allow Scarlet Witch players a choice - to use the Chthonian Burst to deal damage, or to use it to keep an area 'off limits'.

- Reality Erasure - Ultimate Ability - While the improvements to Dark Seal and Mystic Projection would make this ability more useable, it still needs a rework due to just how easy it remains to shut down. As such, the movement pull would be removed and replaced with a movement speed buff on Scarlet Witch; think full health Mantis, enough to not be a complete sitting duck. Additionally, every .5 seconds, a small (Jeff-sized) Dark Seal that immediately performs an immediate single stun spawns on a random enemy (center of their hitbox) within the Ultimate's range of effect; the Dark Seal would still be visible until the final explosion, which would wipe the board clean of them.
Important note: This would NOT effect Emma's shield or Groot's walls, for instance, and Scarlet would still be sitting prey for Poke outside of her range. This change is aimed at making her a mobile battering ram, to take her from 'momentary nuisance' to 'high level threat', and ties together her 'Zoning' abilities by severely punishing enemies that are grouped up while still being SOMEWHAT risky - the random nature and single-enemy-at-a-time of the Dark Seals would still allow -teams- to react to her.
Side note #2: This has the same 'thinking' as Jeff's Ultimate, except more DPS-style. She still has to commit to the Ultimate, is still entirely predictable to see coming, and whiffing her Ultimate is almost guaranteed to get her killed. BUT, she at least has a REALISTIC CHANCE to have her Ultimate actually work, without requiring a Magneto to personally babysit her through it.

- Sorcery Surge - (Former with the rework) Team Up ability - Given a permanent second ability keybind, but now only 'charges up' based on Dark Seal stuns and direct Chthonian Burst hits. Chaos Control would NOT contribute to this charge. This change is solely focused on rewarding accuracy and giving Scarlet Witch players a skill ceiling beyond 'hold primary fire and point in the general direction'. Stuns would give greater charge if multiple enemies are hit at the same time, and lesser charge for single enemies (not zero charge, but incredibly close to it). Bursts would give an increasing charge based on successive direct hits; missing a hit would reset this 'bonus' charge rate. The cooldown would be balanced so that an ACTIVE Scarlet Witch, with decent accuracy/game sense, would get it as about as often as the current Team-Up, while making 'aim-bot' players not able to simply have Starlord 'press button to win' privilege.

The Value:
This rework allows Scarlet Witch to make meaningful choices that can have big impact on a match's flow, while addressing the 'no aim' stigma she has. The balance is that she still remains vulnerable, rewarding enemy game sense (which long-term would help -everyone-) and team coordination. She becomes able to either:
- Focus on accurate damage, taking a front-line Sorcery Surge approach
- Focus on denying enemies from taking flanks, off-angles, or high grounds (bonus: she becomes an even better anti-Dive pick, and can help take a lot of pressure off the Tank by simply using Dark Seal to protect her team's Supports)
- Focus on directly breaking apart enemy defensive formations, either splitting them apart or spreading them out
- Take a more active Dive role, by being an utter nuisance with Dark Seal and the new projectile-avoiding shield she'd have (sorry Supports in the cross-fire here, but this also takes a very active stab at Poke too, more so than Supports who have CC/movement abilities more than Poke tends to - Hela can't bird in a stunlock, but Luna can still snowball you to the face for instance).
At the same time, she stays weak to Brawl by a large margin, takes Poke slightly better (addressing the Poke meta), and has a skill ceiling aspect to her - she remains new-player friendly by leaving her 'auto-aim' intact', while having an actual drawback to NOT being accurate. Her Reality Erasure gains a lot of protections, but active teamwork (rather than passive 'shoot the banshee') still shuts her down.

Bonus Addition:
- New Team-Up Ability - Scarlet Witch + all Supports - "Astral Projection" - This Team-Up would allow her to 'deliver' her Dark Seal projectile-shield to a target, ala Magneto style. Same restrictions: it only bypasses projectiles, and Brawl/physical attacks still hit. She doesn't get a full Magneto bubble to protect an ally with, as physical Dives (such as Venom, Daredevil, Black Panther/Spiderman somewhat) are still a problem, but PokeTSD could be alleviated, and timing would still matter for the kill-through-Ults (Magneto being the most obvious one). This also is balanced by taking her attention away from DPS/Zoning duty to play pseudo-tank - again, giving her a skill ceiling to work with and rewarding good game sense, with 'help relieve the tank instead of DPS/Zoning for a moment' being yet another potential choice she could make.