this game would be better off without the level-up system and only rely on weapon upgrades and such.
Yes. This is my major complaint with every metroidvania including SotN. The level-up system makes the games way too easy. Can't get through a part, just grind for a few hours. Games shouldn't work that way. It should be a contest of skill not patience.
For all the flack LoI got, the one thing it did right is that it didn't have the level-up system. It just had hp, mp, and heart max ups as well as different armors and a few different weapons. The fact was that there was no grinding and when you actually beat an area, it felt like an actual accomplishment because it took real skill to beat it. There was no way that you could become overpowered and there weren't any broken weapons to make use of. This is what these games should be like.
LoS did something similar and that worked. It was a real challenge to beat even on the easiest difficulty setting. Say what you will about the stories, but the game play is what needs to be present in most of, if not all, the games.