It's odd, though - when I increase cursor size in the System Prefs, certain cursor shapes, like the arrow and the hand, scale up cleanly in AP, whereas others, like the brush circles and the pen tool, become pixellated. Ideally, the circle wouldn't scale up at all, since as you point out, it no longer represents the actual extent of the tool. But that may be out of Affinity's hands.
I'm glad you explained why my disclosure triangles were so dim, too. Nice if it could be fixed, but easy enough to work around. (One of the primary reasons I'm dumping Pixelmator is its insistence on using a dark, low-contrast UI.)