Hollow Knight controls feel a bit better, so there are always ways to improve. I'm not sure what kind of ways, but I'm not a designer.
Killing enemies is an abstract measure of time, but makes sure player is actively playing instead of leaving the game on and going to do sth in the kitchen. I've seen similar systems like that in games before, where time stands still and progresses if you take some action.
Hollow Knight is often compared to Dark Souls btw - Soulsvania = soulslike + metroidvania.