What’s been a bit disappointing is DEs getting on the wayland train so late. A lot of the kinks could have been worked out way earlier if they had given their 2ct of feedback right from the start, instead of waiting 10 years to even start thinking about migrating.

That's the real issue. And its worse with Gnome, as Gnome doesn't want support "all of" Wayland and its protocols. That means Wayland will be broken on Gnome, despite Gnome being the most used DE (at the moment). People complain about the problems in Wayland, but not all problems are caused by Wayland itself.

However there were or are two big reasons I can think of why Wayland wasn't adopted early and for some may never: a) its much harder to be Wayland conform, because the window manager/DE has to do much more work, b) Wayland was just not ready before, as many important aspects were missing (in example some basic protocols, Nvidia) or broken. I don't blame them. For the record, I am not a Wayland chill, just talking about this, because there are many misconceptions (me included, I'm not perfect) and switched to Wayland just end of last year. Before that Wayland did just not work for me. I even switched from Qtile to KDE, because KDE has probably the best Wayland support (I hate manual window management).

Edit: I just remembered another reason why Wayland wasn't probably adopted early. Canonical/Ubuntu started a Wayland alternative called Mir (that was before Mir transformed into a Wayland compositor). And devs probably didn't want set on Wayland or Mir before knowing what will be around in the future.