I feel like a lot of your points were true at one point, but are becoming lest relevant.
For one, at least with XFCE, I found myself not really running into DE bugs.
Also, I don't think two years is as obnoxious anymore. During the era of the GTK 4 transition a couple, it drove me nuts, but now that a lot of APIs like that have stabilized, I really don't notice much of a difference between Debian Testing and Stable. I installed and daily drove Bookworm late in its lifecycle on my laptop, and in terms of DE and applications, I haven't noticed anything. I get the feeling Debian's gotten better at maintenance in the past few years - I especially see this with Firefox ESR. There was a time where the version was several months behind the latest major release of ESR, but usually it now only takes a month or two for a new ESR Firefox to come to Debian Stable, well within the support window of the older release.
Also, I don't think Flatpaks are a huge dealbreaker anyway - no matter what distro you're using, you're probably going to end up with some of them at some point because there's some application that is the best at what it does and is only distributed as a Flatpak.
Frankly, I probably am a terrible reference for gaming, as I'm a very casual gamer, but I've found Steam usually eliminates most of these issues, even on Debian.
Also, the official backports repository has gotten really easy. My laptop had an unsupported Wi-Fi chipset (it was brand new), so I just installed over ethernet, added the repo, and the install went smoothly. There were a few bugs, but none of these were specific to Debian. Stability has been great as ever.
In conclusion, I think right around Bookworm, Debian went from being the stable savant to just being an all-around good distro. I'll elaborate more on why I actually like Debian in a comment directly replying to the main post.
I might disagree with 99.999% like you - maybe I'd put it in the 50-75% range.
What do you mean by "window roll-up"?
Also, the settings menu thing is weird - mine takes less than a second to load, and I'm on a machine with a 7 year old processor at this point. I almost worry that if that takes a long time KDE will be more miserable performance-wise, unless you've already tried it on here.
By the way, what distro and XFCE version are you running - just for good measure.
The outdated sentiment is probably based, honestly. I think it's gotten better, but there are rough edges. In the end, do what works for you.