Slavs are a pretty great KotH civ

I've won a few community games (nothing big) with them and I had great experiences.

Cheaper siege and their unique infantry tech make keeping the middle easier than other power house civs like the mongols. Spamming siege ram with halbs and champions is cheap and doesn't put you out of the game if you lose the middle once, but can win you the game if you have good timing.

I just never see them chosen in T90's community games.