Yeah, no FE is perfectly balanced, but some are far more balanced than others. I doubt this game will top FE12 for me.
It's not just the DLC, though. Certain class/weapon/skill combos involving the nosferatu tome can break the game as well.
I don't think it would be hard to implement a scoring system. Yes it would penalize players that want to grind everyone to max stats/supports, but those players are free to disregard the score they're rated at. Maybe if you played the game in casual mode you wouldn't get shown a score at all. That would probably make some players happier.