I thought I would gain more XP in a +2 tier match. But I cant see any difference so far or at least nothing which would worth it to stay in a +2 tier match.

I only make less damage, has to be more carefull, stay behind and cannot fight against all tanks.
Meainig less XP in general and waste of my time.

So to be honest I dont understand why you dont leave in a +2 tier match.