Runners on treadmills don't actually move forward.
If I assume your point is true, wouldn't everyone then just switch to Paint for all 2D picture editing? I mean it's the fastest - opens instantly on my machine vs 3-4sec for Krita/Gimp/Photoshop. But it's also bare bones. So why isn't Paint universal used by everyone?
My assumption: what people want is to not waste their time. If a program is 3 seconds slower to start/edit, but saves you 45 minutes of fucking around in a less featureful editor, it's obvious which one is more expedient in the long run.
That's kind of my point. Even you eschew Paint's simplicity when you need a more complex transformation. Nothing you do in Paint.Net isn't impossible in Paint, given enough calculation and preparation. So a performance isn't the deciding factor. It's the speed of achieving thing X (of which startup/lag is a tiny cost).
Similarly in Paint.Net you could emulate many Photoshop features (e.g., non-destructive editing), but doing so would be tedious (duplicate layer, hide layer adjust copy layer, then edit until you get it to where you want it).
There are two things in play: just because it's a deciding factor for you doesn't mean it's a deciding factor for everyone else. Second, even for you, Paint isn't enough. You also got Paint.net. You can reproduce almost any effect in PS or Gimp or Krita in Paint/Imagemagick. Why not just use those two for everything.
It's the same thing as using an IDE vs notepad(++). Anything done in the IDE behemoth can be done in notepad. Albeit at a significant time penalty, and with way more CLI jousting.
> I use Ctrl+Z for non-destructive editing in paint
That's not really non-destructive editing - that's Undo. A non-destructive editing means you can edit, change things, save, close the program. Reopen file after X days amount of time, and change effect or thing you applied.