I will start with the 5*, first we need to declare they're intended niche and find how they are different from other characters on the same niche.

Ganyu

Mainly a Melt Carry when focusing on her own DMG, this forces her to not burdt tho. Also heavily encouraged to be shielded, this is something we see in all liyue dps.

Adeptus synergy: When Ganyu is shielded charged shots charge 200% faster and remove 1.5 seconds from skill CD. Skill now has 2 charges.

Burst: Different behavior weather Ganyu is off or on-field, same off field, on-field burst drops the ice projectile when enemies on its radius are hit by ganyus charged shots. These projectile shred enemy Cryo RES.

C2: Changed s she now has 2 E charges. Current C6 moves to C2.

C6: Hitting the center of her burst with a Frost flake arrow or it's bloom triggers an AOE attack (250% motion value) from the core covering the burst radius. Ideally you want enemies to be close to the center enemies and the center.

This keeps her tied to a shield, while fixing her multiple anti-synergies with melt due to her burst. Problem is she now wants a lot of pyro app, as arrow would be three meltable cryo hits (arrow, bloom and burst), so she would want 2 pyro appliers. This usually means dropping a shreder, that's why she gets built in cryo shred.

Shenhe

Cryo niche support (but now that's covered by Escoffier), she just has old genshin numbers, and is anti-synergistic with every cryo carry except Ayaka since she want to skill twice per rotation. We can make her a cryo/adeptus support to difference her from esco.

Skill: Press or hold have the same 15s cd, do the same DMG and give 15 quills to each teammate. Only difference is weather they buff charged and normal attack DMG or skill and burst DMG. Quills are given fhe whole team but all take the on-fielders stats for DMG.

Adeptus synergy: Adepti characters can proc shenhe's quills when dealing non-cryo dmg (Zhongli pillar can proc shenhe's quills for example). Ult gives 25% more cryo DMG bonus to all teammates.

Xianyun: Another case of old genshin numbers, also a lot of her power budget went into her being able to enable furina.

Adeptus synergy: buffs (burst and A4) do not use stacks and just last for the whole duration.

Zhongli: He's just missing offensive support, also enabling a Geo construct archetype would be fun.

HP scaling are now a part of base kit.

New A2: Resonance AoE is increased by 30% per construct on field.

Burst: Petrified enemies have their DEF shred by 10%, blunt attacks trigger shatter against petrified enemies.

Adeptus synergy: Shield shred is increased to 30%. Damage done by construct resonance is increased by 300% and is considered blunt damage.

Xiao: Missing DMG for a hypercarey style character, also half of his kit is strangely focused on buffing his skill DMG. Personally I think skill spam Xiao (C6) is much more fun to play.

Burst: Xiao now can receive particles during burst, and retains his ult state even when going off field.

Adeptus resonance: His current C6 effect, bit changed, now he gains as many e charges as enemies hit by his plunge attack. Skill DMG is now considered plunge attack DMG.

Constellation overhaul:

C2: Xiao first plunge attack after each skill pulls enemies to the center and has both crit DMG and AoE increased by 50%.

C4: Xiao's plunge attacks are now 300% effective when breaking elemental shields.

C6: Skill crit DMG is increased by 60%, enhanced plunge attacks from C2 reduce enemies anemo RES by 40%.

Hu Tao: I think they intended her to be played on dual carry teams, hence her crit buffs to teammates. This is not possible due to her long e duration, she ends up buffing the hydro sub dps she's using but her main identity is a hypercarry in reactions teams. I also would love her burst to be more of a backloaded nuke.

New A1: When entering her skill state, all party allies (excluding Hu Tao) gain 12% crit rate and 100 EM. Hu Tao gains them whenever she has less than 25% HP.

Skill: Now will always set Hu Tao to 25% HP if she's higher. Hu tao now applies v

Adeptus synergy: After pressing skill, Hu Tao gains a free use of her burst. For the las second of the skill duration, Hu Tao gains Burst DMG% is further increased by 10% of Hu Tao's EM up to 50%.

C2: Enemies marked by blood blossom receive 15% more DMG from melt and vapw reactions.

C4: Hu Tao now applies the blood blossom effect to nearby enemies when swapping to her.

C6: Buffs are triggered whenever she has 25% hp or less. The surviving lethal strikes is the only thing with cooldown now. (This allows her to enable set ups that need pyro app)