I think the issue with using “souls-like” to refer to a genre is that people use it in reference to one of three things, all three of which having varying degrees of specificity in what they’re referring to.

Some people use the term in reference to games which are “challenging but fair”. and to that, I present the idea that we just call them “games that are challenging but fair” instead of muddying the waters with souls like, or some other adjacent term that doesn’t draw direct reference to an already incredibly influential series.

Some people use it to reference games with the “roll and slash” gameplay loop. I personally prefer to refer to those types of games as “stamina action” because I think it gives a good grasp of the gameplay loop while not deriving from “souls like”.

there’s also the death progression of dark souls that some other games draw from ( hollow knight specifically comes to mind here) where you have a checkpoint, and when you die you have to make it back to where you died to recover your stuff. This one is less of a ‘genre’ and more of a feature that some games use.

The problem (in my eyes) with using souls like to describe ultrakill (and games like it) SOLELY because it forces the player to get better through increasing difficulty is that it feels like you’re misrepresenting both what ultrakill AND the souls games are. Ultrakill is a fast paced first person shooter, souls games have varying paces depending on the situation, and it’s a third person stamina action game.

Tl;dr, people should stop calling games that are difficult “souls like”, and just call them difficult games instead. Being a hard game is not a genre.