The only thing I actually liked from Cosmic is the ability to remove rounded corners, which is something I hate that we're forced to endure in every single UI at every single level. Even KDE seems to lack that, even though they give a few options for the UI. (Edit: I mean, as far as I saw on Plasma, KDE doesn't have the option by default. Maybe it can be added or something, but I didn't see anything in the settings to indicate I can remove rounded corners.)

Tiling is just not to my liking, but maybe it's because I don't use huge monitors, so every time I tile a window everything gets bunched up or cut off. Maybe I'll think differently when I move from 24" to 27", who knows. I ended up disabling tiling and stacking in Pop! OS 22 and just use vanilla GNOME snapping when needed. Stacking also adds a horrible tab UI that can't be edited (say, make it vertical instead of horizontal), as far as I know.

So, to me, the DE just doesn't add anything different or extremely necessary. But of course, I can only speak for myself, my tastes. I'm generally very picky and an outlier in most things, so I'm not surprised other people find those things to be essential.