I have commented on this ingame every time I played the map (which is 3 times in total), but only as short one-liners, so I'm gonna type out a longer post.
It's far too compact for any quality battle.
Picking heavy, going up the stairs to the left and jumping down from the balcony there, you have successfully managed to deploy a murder machine with 300 hp and no reloadtime in the middle of the enemy team within seconds(!) of the round starting.
The heavy is a VERY powerful class when there are no open spaces. His speed is the disadvantage, but it's completely nullified here. A medic heavy combo is even more destructive.
Scout is the opposite, and it shows.. you can't use your speed for anything much.
Sniper is pretty useless, I mean sure you can snipe. But when you know you'll get rushed and pushed back into your spawn in a matter of seconds, you might as well roll another class and be useful.
Basically: There is no class balance due to the size being minuscule.