What is the point of me having 256 GB of storage on the phone, if the phone starts slowing down wholesale once I take 50% of it? I get that there needs to be some buffer for swap and flash magic and whatnot, but I'd thought it would be closer to PC / Windows, where everything is fine until ~90% storage being used.
That's on top of bloated software doing background magic. Can't speak for other phones and brands, but my experience with Samsung flagships (S4, S7, wife's S9, now S22) is that the camera and gallery app are bloated, and their performance degrades rapidly with the amount of photos you take - around 50% worth of storage is when camera starts having delays on the order of seconds, interfering with its core purpose of taking photos.
(And it's not that it couldn't be better - Samsung just isn't investing effort in making core system apps performant enough. It's hard to find efficient apps these days on the Play Store, but there are rare exceptions, like e.g. Aves gallery, which is FLOSS and manages to be leaner, faster and significantly more feature-full than just about anything else, stock or third-party.)