I think its too late now, but imo I think B1 and B2 shouldve fought A5 and A6 before quarters.
But now its more fair to make A3 and A4 fight A5 and A6 in the quarters, because it rewards A1 and A2 for coming 1st and 2nd by giving them worse opponenents in quarters (aka B1 and B2) - it also punishes A3 and A4. Like why would A1 and A2 be given harder matches in quarters than A3 and A4, it would literally discourage teams trying in the group stage
I agree it shouldve been different and a bit more rewarding to the top of div B, but at this stage, it cannot be changed if it wants to remain as fair as possible