No, that is not the only cure. Better aim is another: headshots kill Assault in one bullet just like everyone else. Or, if you have the M4, you only have to get in one more shot than them. Or use Boost to suddenly make him miss. Or draw him into an area where there's airbots, turrets, or C4. Co-ordinate with teammates. Drop medpacks ahead of time so his health advantage isn't there. Or die, but bog him down so long he's not helping with his team's objective. Etc. etc.
There are many, many ways to kill Assault units, or to make them useless to their team. I get killed by them a lot, but I've also had the pleasure of hearing Assault players whine over prox chat "How the hell did he kill me?!" because they mistakenly believe (like you evidently do) that Assault is an invincibility suit. It isn't.
All this applies even more forcefully to friendly-fire servers, where idiot Assault players hurt their team more than help it.