Yeah, I came to the same conclusion a few months back. Sadly I had to ditch KDE for GNOME due to an issue[0] specific to NixOS but after going through the gauntlet of tiling window managers and PaperWM/Niri over the years I've also settled on a traditional DE.

[0]: https://github.com/NixOS/nixpkgs/issues/126590

I'm surprised to hear that niri didn't work for you, I feel like it's a really good middle ground between tiling and floating window managers. It handles a lot of window resizing and arranging for me, without being too rigid. Windows can have any width they need without having to evenly divide my monitor.

In sway, put the lower priority windows in another workspace, or the scratchpad, or in tabs/stacks. You can bind keys to focus specific programs by their appid/class also, so even if they're on another workspace or monitor it'll jump right there.

It sounds like the scratchpad may be especially close to what you want.

Maybe awesome-wm would be better for you then.