I just installed Kubuntu last week so I could get the additional shift-drag targets to split my 34" ultrawide into 3 sections, or bump to the edges for the half filled.
[1]: https://github.com/esjeon/krohnkite [2]: https://github.com/paulmcauley/klassy
All the rest I'd prefer to just summon as-needed and then dismiss without navigating away from the windows I care about.
sway/niri want me to tile every window into some top-level spot.
Took me a while to admit it, but the usual Windows/macOS/DE "stacking" method is what I want + a few hotkeys to arrange the few windows I care about.
It sounds like the scratchpad may be especially close to what you want.
I don't want to leave the workspace nor go find which tab/stack I've put Spotify just to use it. And scratchpad is no better since I'd have to do an explicit summon/dismiss cycle between workspace and scratchpad just to recreate behavior I already have on a normal desktop env.
But it answers the question of:
"Alright, whenever I want the $app window, I just go to column X of workspace Y"
Which isn't something I want for 99% of the windows I have open.
Most of my app interactions are transient where I prefer "summon $app from the ether without navigating anywhere".
For example, here are low priority apps I have open: calendar, discord, whatsapp, notes, journal, database gui.
Niri would make me find a place to put these apps in the top level and then navigate to them which doesn't match their transient nature.
I'm fairly sure you could use scripting to come up with a Niri workflow that worked for your use case. Maybe something like niri-scratchpad (https://github.com/Vizkid04/niri-scratchpad). But I sympathize if you don't want to spend a ton of time experimenting with your tools when you already have something that works for you.