I too think Cinnamon is a pretty great Experience. I am using KDE and heard from many people that it feels better, its more unified and has way more features.
Wayland is important for security, and Mint will need a long time to adopt that. There are already apps only running on Wayland for reasons.
KDE is a bit unstable as its a huge project. I hope that will get better in Plasma 6.
I sure wish to have something like KDE more stable. But once you are used to it, its just better. Things that are not there yet on Mint are on KDE since years.
Its a bit of a mess as its so old. Extensions need to be cleaned up. But like, Dolphin extensions are so great, I dont know an equivalent on Cinnamon.
Also the distro model is the standard one. A Fedora Atomic Cinnamon variant, with modern presets and everything working, would be a great thing to install anywhere. Automatic atomic updates, easy version upgrades, transparent system changes and resets being just one command away.