We need to fear Soldiers going solo, Engineers not doing their [censored], and Medics going rambo with self-revive
Soldiers will end up dying, which will in turn make them want to stay back and play more strategically and go for the objectives for XP
Engies will put a sentry, and with the sentry up they still get XP from the kills (if i saw correctly from containter city vids) so they will be able to stay back and buff the teams guns
And medics won't go rambo with the self-revives because there's a limit to when you can revive yourself and they get more XP by reviving the team
I wouldn't worry too much about that stuff. I'm sure it will be fine because when people see that going Rambo won't get anybody anywhere, people will think more team based. If anything it'll be a trial and error with the players. I haven't seen many objective based games have people only running out for kills. The only games you see people doing nothing but killing is CoD and that's only because that's where all the rewards come from. With a game that rewards less for killing and more for teamwork people will catch on to teamwork quickly.