It's weird how uncreative froyo was. I guess they really are used to sticking with one class for an entire game.
Defending last with several demos is trivially what they should do, outspam the pyro/short circuit engie whatever. When the cart is barely capped in the first round 2nd point, going spy and short circuit-ing away the stickies is something they could have done to cap the point quickly.
Uncle Dane should not be full time engie, on defense the tele is useful, but the sentry is nothing against a coordinated team. Running 2 meds is very important, and other than nursey all the other players should play med when needed. In general respawn time should be spent not only on spectating other players but also on figuring out the most suitable class to play next.
I think ideally a double demo, double medic, double sniper on offense runs fairly well, one medic with vac, and one demo on cart with pain train.
But that's just my opinion, feel free to comment, I'm down for a good discussion, this mode imo is really interesting