Your problem is this:
I have no way of knowing which bodytype to pick before I join a game. As such, if I’m being fairly casual and join some random game it’s reasonably likely that my team will consist of a random selection of bodytypes. This is pretty much guaranteed if the teams all swap about each map in order to sort the storyline-order of maps out.
If the choice of bodytype is advantageous, then this advantage will be randomly distributed. My team might happen to have an easy time because we’re built to the task, or our balance might be hugely off.
If the bodytype is not advantageous, then no-one will care because by definition it doesn’t matter.
If you don’t let people change bodytype dynamically as a tactical response, then you’re left with two options:
- Bodytype is simultaneously unimportant and random.
- Bodytype is simultaneously important and random.
In scenario (1), you may as well drop the bodytype thing entirely because no-one will care.
In scenario (2), people will change characters and rejoin with a bodytype that works. If they can’t do this, they’ll disconnect entirely and join another server over and over until they get a combination that does work. Don’t underestimate how snobbish scrubs can get about how everyone else on the team didn’t pick the right bodytype.
Look at Random Arenas in Guild Wars to see this in effect. Look at what happens when four Elementalists end up in the same random team - they all quit and immediately rejoin in the hopes of getting a plausible team build. Randomness doesn’t work when it’s applied to anything important.

or the first damage you receive will be absorbed by the medic that revived you, or, or … …