v3 taking much more screen space away for toolbar than v2 (same Qt, dpi, …) and ignores global Qt theme/styling

I’m attaching two full-screen screenshots from my laptop (yes, this is literally all the display size I have, and yes, my window manager really only draws a one-pixel border around windows and that’s it) running MuseScore 2.3.2 and 3.0.2 “side by side” (started at the same time, but on different virtual desktops).

I’ve tried to position the mouse pointer into the same place for both screenshots, for comparison (or go measure pixels in gimp or something), and I’m showing the settings so you see the pixel icon size is the same.

… versus…

xrandr says: LVDS-1 connected primary 1024x768+0+0 (normal left inverted right x axis y axis) 246mm x 185mm (that is about 105.73×105.44 dpi) which (just tested with a ruler) indeed fits.

xdpyinfo, though, says:

screen #0:
  dimensions:    1024x768 pixels (270x203 millimeters)
  resolution:    96x96 dots per inch

That being said, if I run either xrandr --dpi 80 before MuseScore 3, or it with -D 80, the sizes become somewhat manageable (the upper bar still uses much too much space, but the lower bar shrinks, almost too much), but the score is much too small then; with forcing 96 dpi, the score looks manageable.

Hmm… indeed, changing the DPI changes the icon sizes, but not the dropdowns, so it looks even more clunky.

And why is the style of the drop-downs different between these two, anyway? Shouldn’t that be taken from the global Qt theme? The background colour of the menus also differs (grey in 2.x, white in 3.x which is really not well distinguishable from the white of the score paper/background and massively sucks from a UI/UX perspective… it looks about as crappy as a GTK+3 application instead of like a proper Qt application). (In contrast to e.g. qasconfig, it also ignores -style motif.)