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This isn't strictly related to your suggestion, but a more general comment.

Am I the only one who finds it a bit frustrating that any time someone complains about missing/bad functionality in gnome, someone recommends to install an extension, but when a user complains about stability or performance, their number of extensions are blamed?

No you are not the only one. I've had performance problem with GNOME on my Dell XPS 13 for a while. Initially it was mostly sluggish animations. After couple of years, with regular updates, my fan is continuously spinning and it visibly feels slow. I don't use very few popular extensions (hide title on maximize, the ubuntu defaults).

I mostly use i3 which is perfect, but one of those days when I feel like using a full desktop environment, I just can't. On positive side however, scaling for hidpi screen seems to work out of box in Ubuntu 18.04.

It works for me just fine in a 2x2 grid

Not in my hands, no.

Odd, mine works. Are you perhaps using wayland?