• KDE is the best if you want customize without editing yaml or xml or you just new to Linux
• XFCE, LXDE, MATE, & CINNAMON are the best if you have very old system but still want to have some customization.
• I3, SWAY, & OPENBOX are the best if you feel need little bit challenge to customize
• NO GUI (CLI) is the best if you feel DE is bloat or systemd is bloat or wanna feel like Hollywood movie hackers

I think latly, especially in plasma 6, KDE got as viable on old machines as XFCE and surly mint and cinnamon.

Yes and no. They should really separate the fancy stuff from the base stuff. Like have a kwin-wayland-base and kwin-wayland-extras.

I guess some other features are not easy to rip out, but having only simple animations etc would really make sense.

I will try Plasma 6 on an Intel core Duo in some time though, exited.

They have an issue with disabling not needed stuff. XWaylandVideoBridge, legacy app tray support, GTK global menu adapter, and other cool but edge case stuff is just always running in the background.

Same for accessibility, GUI keyboard and Orca, even though they will be somehow dynamically loaded, they are not controllable transparently by the user.