Perhaps not so relevant on public servers: which of these do you think is better for the team?
a) adaptable players who switch classes to whatever type they think is more relevant given the current situation or
b) players who specialise in a single class
For instance, if I there’s a player on my team who I recognise as being an exceptionally good medic, I can adjust my play accordingly and we all benefit. But it can be frustrating to look around and find that he’s switched to some other class…
Of course “specialists” need to at least have a rough idea of the capabilities of all the other classes (and the better this appreciation is, the better they’ll be able to play their own role).

but I think it’s the fact that you have to go strip someone’s uniform in ET, whereas in WT you could just choose the enemy class you wanted to impersonate, which is too easy).