fail team is fail. You can't get past 5 engies all camping? Seriously, do you not know what ubercharges are? Even a decent spy and some non retarded combat classes would be able to take them out with minimal effort.
In my experience, we stomped teams that tried to stack (scout rush comes to mind), and the teams we had trouble with were the well balanced ones (we ended up winning btw).
If you want to go for it but imo, let the n00bs stack, just makes it easier for us to win again

BTW: Will we run arena maps next time? I think arena would be more suited to 5v5, but it is a compltelty different kind of game to vanilla TF2
Also, only 1 medic? Doubling up on medics just for prep phase for 2 ubercharges is quite a legitimate strategy.