I’m not sure what you mean saying “gimp being behind the times” compared to photopea. Gimp absolutely blows it out of the water in terms of being a useful tool.
There's sure something to be said about OSS projects and release health/hygiene. I'm not qualified to synthesize and say it, but I know which of my daily-driver projects release frequently. And I know which ones don't, and which ones my [distro] and others patch around because they can't bother to tag + publish releases, or lack the discipline to know when to ship.
I fully expect GIMP to ship gtk3 support after gtk3 is deprecated, at this point.
When wine, an entire, very functional win32 re-implementation and proprietary s***-a** discord is your brethren, it's a bad sign.