I think the saddest thing about “flat” designs is that technology is incredibly capable of delivering so much more. Sure, in 1988 we only had a few colors available in hardware so maybe a button had no choice but to be one boring solid color. In 2021, though?!? Ultra-high resolutions, massive color palettes, photo-realism has never been easier to achieve (even in 3D!!!), all this computing power, and then these overpaid “designers” give us: boring square buttons with one color with unreadable contrast. We deserve so much better from modern UIs.
UIs should not be so plain and spartan that they are literally unusable sometimes. Every Single Button should look like a button, with way more detail than UI buttons have ever had before (why not have a ridiculous number of colors in gradients to make buttons truly beautiful?). When something is highlighted, I want it to be obvious and, again, beautiful (why not glow with photo-realistic lighting effects, for example, since we clearly have the ability and can spare the processing power?).