In terms of raw power... Id say Victoria is also very good conteder.
If we ignore Bloomed forms, which dont mean a thing for us Nutaku players for a long period of time to come that is.

She has a solid AOE ultimate, and both her passive are Full party wide Buffs. Very solid statline.
In terms of raw power she definitely is up there.

But yes, atm Sakura is indeed one of the most powerfull characters with solid party buffing. The strongest ? Not necessarily, but definitely in the top 3 contenders.