It's a dirty move, the only solution is to top up or wait for the merge I guess.

I'm having the same problem but in my case it's even dirtier. A bunch of p2w from one group are doing what you said and feed their win streak to their weak members, those weakling after got feed exit the battlefield in order to be safe.
That group is example of group hoarding, play dirty and cancer of this game.
But nothing can be done about that except for merge or one of you guys top up and beat them in term of money.