My issue with this is not that they're getting rid of buggy applications they don't want to support. It's that GTK 2 itself is not buggy and has no problems. There are still plenty of people using GTK 2 applications and I personally wrote a handful of new GTK 2 applications over the last year. GTK 3 wasn't a replacement for GTK 2. Just like GTK 4 isn't a replacement for GTK 3. They're separate things.

Dropping buggy GTK 2 software applications: okay, understandable.

Droppping perfectly functional GTK 2 itself: not okay.

Other distros like Arch have well supported unofficial repos that still provide the GTK 2 package when it is needed. Debian does not. It does not hurt Debian at all to keep packaging GTK 2 itself and making it available. It is stable software and there have been no changes for decades besides a handful of compiler args to deal with changing compilers.

And GTK 2 does not need to support HiDPI or native Wayland. Just like all the Wayland programs do not support running on xorg or even other wayland compositors not sharing their wayland protocol extensions used. This is not actually a show stopper problem. It is consistent with other software's incompatibility with waylands and would only apply to those actually using GTK 2 applications and those demographics likely aren't wayland adopters.