Your wording has a lot of weird question-begging in it: “not include a fully functional save system,” “remove the save feature,” etc. This isn’t an accurate representation of what it’s doing and makes it harder to talk about unless I just ignore what you actually say. The games do save, and typically they save constantly, though HK and Silksong don’t save your location in an up-to-date way, they tie that to designated save points (like almost all games with save points do). Dark Souls though actually saves your approximate location anywhere in the world so long as you’re not in the air or something, which is more than most games do. Regardless, both series do save lots of other information about the world, like gates opened, items retrieved or spent, non-respawning enemies and bosses defeated, NPC quests (but typically not if they died in a fight alongside you, which again is generous), and the currency isn’t “not saved,” the information isn’t lost, you just get a penalty that you don’t like. It’s fine to not like that penalty, but it makes things difficult when you describe it incorrectly.

Trying to address what you’re saying here particularly: I don’t think that makes sense as a criticism. Games usually aren’t made with a bunch of modular parts in the core mechanics to switch out, and they are designed based on the systems that they use. Dark Souls would mostly become harder if you had conventional saves instead, because you would need to make it back alive to a save point for your progress to be saved and otherwise it’s just dust in the wind if you open a shortcut but you get killed right after. If you could toggle systems, that would be confusing and harebrained for basically a trivial benefit if you understood the system, because as DS is designed it usually wouldn’t even be a good idea to use normal saves for boss runs, because you still might die after you beat the boss and then you need to fight the boss again.