Actually at some point in recent years i used NeXTStep and having being using Window Maker for many years by that point, i felt a bit of an uncanny valley effect: what i was looking at the screen felt very familiar but still somewhat "wrong" and a ton of what i was used to didn't work (or worked in a different way) :-P. It made me realize what the people around the mid-2000s who tried various Aqua-like themes on GNOME 2, etc and said that it looks off/wrong were feeling like :-P.
EDIT: also i think Window Maker is not the only window manager that supports/uses dockapps. I think FVWM and Afterstep can also use the same dockapps.