Reading through the forum, I noticed that @oberon has expressed his frustration at the rapid rate of change as regards the Deepin DE - he said, I believe, that he wasn't going to be packaging Deepin anymore until it stabilised. I'm still receiving Deepin updates, though, so I decided, more for fun than anything else, to install Kwin again and see where it takes me. I'd had Kwin before and was horribly disappointed. Not sure if anything has changed - I don't recall the version number I used then...
but I tried it yesterday and I actually liked it. Performance is drastically improved. Manjaro now eats up something like 800MB of core with no apps running; when I was running Mutter, it ate between 1.2-1.5GB. Animations are more polished - for example, dragging an open window makes it translucent, in keeping with Deepin's blur fetish. Workspace switching is easier. Pamac looks good now (I hated how it looked with mutter). Windows now "snap" properly, to the left edge of the screen (but I have been having problems with the right edge forever - even under Ubuntu).
Downsides: The blur checkbox in Terminal still doesn't work. Small frustration, but it's there. Worse is the fact that Kwin's animations etc. degrade over time, start to stutter horrifically, and I have had to log out and back in twice over two days, just to keep the computer usable. I don't know if it's something specific that triggers it, or if it simply "rides up with wear". Will experiment to find out.
All in all, kwin coöperates nicely with Manjaro-Deepin now and would actually be a good environment in my opinion for someone who likes to live dangerously. I'm not sure if I'll be keeping it on my production machine, but I'm leaning towards yes. Has anyone had this experience recently, good or bad?