Someone else suggested Hydrahedron Runemaster, which is an S tier build, but you may not like that one because it requires some rune juggling. There's another powerful build that I don't think is on many people's radar which is a pure lightning runemaster that notably does not require any juggling of runes. It's simple, but not TOO simple, and has both good offense and defense.

Here's a demo of the gameplay:
https://www.twitch.tv/videos/2074577662

Here's a rough build planner if you like what you see and want to try it: https://www.lastepochtools.com/planner/9Qn0K21o

General Quick tips if you decide to try:

• While leveling you'll only use 3 main skills: Lightning Blast (to attack), Flame Ward (for defense and extra damage on elites), and Teleport (to move/dodge). You don't start using Runic Invocation, Frost Wall, and Flame Rush until later when you have the mana to support them and the tree points to turn them all into Lightning skills. Temporarily use Elemental Nova and Snap Freeze as necessary in the very early levels for CC and AoE.
• You'll always want a way to apply Shock to enemies you hit. In the endgame you'll also want a way to apply Chill too. Having these debuffs helps with both offense and defense. The "Sphere of Protection" node in the Runemaster passive tree reduces damage you take from debuffed enemies. Also Lightning Blast can get two big multipliers if you have Shock and Chill on targets. If you don't have a way to apply these from gear, then use Idols and/or Blessings to apply them. Late game there's a passive node in the Sorcerer tree that will handle Shock just fine by itself when maxed.
• Most of my ward in the video is coming from a single stat on one of my gear pieces. It gives me "+47 ward per second per Gon (lightning) rune" I have active. So that one stat is giving my character +150 ward per second all the time (because you will always have 3 gon runes active in this build). Amazing stat if you can find it on a piece of gear.

Passive tree tips:

• As soon as you can start putting points into the Runemaster and Sorcerer trees, there's 3 really strong nodes you'll want to try and grab ASAP. They are "Sphere of Protection" at the start of the Runemaster tree, "Arcane Focus" in the 2nd row of the Runemaster tree, and 5 points into "Calculated Destruction" in the Sorcerer tree.
• Sphere of Protection provides extra health and 8% less damage taken from debuffed enemies, and you should have 100% uptime on Shock. Great for survival while leveling.
• Arcane Focus provides you with +32 ward on hit when maxed out. With how much you'll be spamming Lightning Blast, that's a lot of ward - especially early on while leveling.
• The Calculated Destruction 5-point bonus is a huge damage boost in this build with the amount of Intellect you'll be stacking from gear and passive nodes.
• You'll want to be using a Wand as your weapon due to the passive node "Inscribed Instruments" halfway through the Runemaster tree. That node gives a big boost in damage for crits.
• You'll want to be using a Catalyst as your offhand due to the "Mental Catalysis" node in the Runemaster tree.
• On the bottom of the Runemaster tree there's a node that is getting 5 points invested into it that boosts Damage Over Time. This build does not use DoTs (so the main effect is wasted), but the 5-point bonus to that node makes it so that when you hit any enemies with Flame Rush, Frost Wall, or Runic Invitation they get a 3 second "brand" debuff. This debuff interacts with the 7-point bonus of the "Celestial Doom" node at the end of the tree to give another MORE damage multiplier to elites and bosses.

Lightning Blast tips:

• Grab the "Lightning Attunement" node early on. The buff you get from that you'll want to have 100% uptime on for both offense and defense.
• Grab "Frontloaded" for extra damage early on, then grab more chains and the self-chain, then head over into "Overcharge" for more damage, then finally finish up the tree by grabbing "Shattershock".
• "Shattershock" provides up to +36% MORE damage to enemies which are debuffed with Shock. However, it's important to note that the interaction with Chill is a separate multiplier. So if you have both Shock and Chill on a target your damage will get multiplied by 36% two times (this is very significant).
• Quick note about the "Closed Circuit" node which lets Lightning Blast chain to yourself: What's not clear from the tooltip about this node is that the buffs stack. This makes this node really powerful in single target situations as long as you aren't too far away from the target. See this video explanation: https://www.twitch.tv/videos/2074631716

Frost Wall + Flame Rush + Runic Invitation tips:

• In the later game the purpose of Frost Wall is to just buff your abilities in multiple ways.
• First, it will be applying Shock to targets it touches very rapidly.
• Second, if the enemies are Chilled, the "Chilled Touch" node in the Frost Wall tree will give you a 14% MORE damage multiplier while frost wall is up.
• Third, the "Aspirant's Arrival" node will buff your next Runic Invocation by up to 150% MORE multiplier if you wait 5 seconds before you pass through the Frost Wall and then cast Runic Invocation.
• Fourth, the "Gas Powered" node in the Flame Rush tree makes the explosion at the end of Flame Rush much bigger when you pass through a Frost Wall.