welp she's gonna be an issue (hot as fuck though and she's the fire princess too lol), he's gonna need a training montage
He needed one from the beginning. As soon as he was chosen as the ring king and it was clear that he didn't have the necessary strength, he should've started training immediately. The sage saying "go collect the rings" is kinda bull, esp because there doesn't seem to be much of a time pressure.
Even if the rings provide such a huge power boost that training's strength boost is negligible, he needs the technique with which to handle the rings' power. We've seen that he's useless in a fight, and I'd say it's just as much (if not more) because he doesn't know
how to fight as because he isn't strong.
TLDR; he needs to learn how to fight properly regardless, so a training montage would've come at some point anyway. (imo there should've been one much earlier than this, somewhere around chapter 3)