A few suggestions at current I believe for Base TC are:

Give all their Commanders 2 Movement or modify the statistics to reflect being the slowest leaders in the game (no other commanders have mv 1)

Give the Celestial Master +1 Astral, either adjust the cost or change the paths to fit it in.

Adjust the gold and/or resource cost of the standard heavy troops of TC.

As of right now they have terrible long weapon units (Glavies and Lightly Armored Pikes).

I'd have to wait and see exactly what the effects of the new and improved HorseArcher orders of Fire and Attack, which will hopefully fix that particular aspect. It might have more of an impact on balance than I could say.

Change the Celestial Servant and Celstial Soldier's paths to cast to be able to be summoned without having to rely on Random picks.