I don't think it's the new synergy buffs. I think it's just Iron Will the problem, if it's a problem. Also, I would have lost a couple of times if I would not have had Wyrmlet's potion ability.
Aside from that, I think that the game should not have a cap for enemies' stats. Or, alternatively, it should find other ways to raise its difficulty indefinitely. Like, adding more effects around, maybe (stunning is always a problem, especially to Iron Will).
Players will always find some strat to reach maximum power. It's the fun part of the game. If you find a way to escalate power indefinitely, it does not matter what the player finds, there will always be a greater challenge.
Alternatively, you could put like, some crazy cap to "infinite" mode, like a special 100 loops final boss or something! XD After HOURS of play, one grows tired of the same run and wants to change. Very few people would like to actually go on indefinitely forever with the same run.
But I'm talking from a personal standpoint, you should ask around.