not really because if you are level 20(max) then you can have 5-8 abilities to get. there are about 12-16 per class. so you will choose your abilities for 1 class and 1 class only if you change you wont be that good. You sir are INCORRECT
Er, actually if you're level 20 you can have 20 abilities, I'm pretty sure. So, unless you like all of your class's abilities, or need a bunch of universal ones, there is room for about two specialized classes per character, it seems.
Also, I changed my vote from medium Resistance medic to medium Resistance engineer because there weren't enough.