The problem is "historical" squads that refuse to split up to even things out. It doesnt have to be literally numbers even, sometimes one highly skilled guy can even things up while the numbers are not equal. When Shane or ManeTMP or Leviathan are in the CT they are worth an extra 3-5 guys (or more) for their side so you have to consider the relative skill levels too not just the raw numbers.
Its JG54 now, but before that it was VMF312, before that it was 78th FG, before that it was JG3, its not a new problem that has come as a result of JG54. Some squads in the past like VF17, VF27, and now JG2, were willing to switch, which is why you will largly see most of JG2 flying allies.
I think the axis squads were outnumbered for so long (and they were) that now they want to extract their pound of flesh to get even. The only problem is there is almost nobody left in the arena to punish and the ones that are there dont stay long.