One of the reasons some trainers won't sping for beans upright is they have "Washout" n the wings. The wings are purposefully bent so that the wingtips stall later than the wing root. That makes it very difficult to get the plane to spin upright, but inverted spins are easier.

The flat bottom wing really isn't the reason for the spin being difficult.
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You can help prevent the overspeed condition which leads to the wing folding. Use a longer lower pitch propeller. Most people THINK you have to use a 10X6 on a .40 size trainer. Try a 11X5 or 11X4 or if ground clearance allws... 12.25X3.75. It will seem like a whole new airplane. Almost all aerobatics will be improved. Most .46 powered (.40 size) trainers can climb straight up out of sight (if you let it) using the 12.25X3.75. The longer lower pitch propellor will act as an airbrake in dives. It will also help you slow down for smoother landings.
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What a trainer can't do? It can't do the maneuvers as CLEANLY as a plane designed for them. I've seen .40 class trainers do just about any maneuver you can name. One of my favorite things to do with a Dynaflite Butterfly (99 inch span .15 powered) is laps around the traffic pattern inverted. (it is NOT easy but it is possible.)