From illustrators to matte painters, photoshop is probably the most common painting app you’ll find.

>People don't generally paint in photoshop

EVERYONE uses photoshop in the painting/art world. Seriously, almost everyone. It's the best app for it, and the only reason people use others in my experience is because they're either free or a one-time payment. Or, because they're painting on a tablet, where (the full) photoshop isn't available.

>while ProCreate is about natural-looking brush painting

This is also not true. People use procreate because of the simple UI, nice gestures, tailored to iPads, for a one-off payment - and because its simply just the best option available on iPads. There's no difference in what you can do with brushes, or "naturalness" between them. If anything, photoshop is better at natural-looking brush painting. If you're wanting natural looking brush painting, also check out the lesser-known Rebelle: https://www.escapemotions.com/products/rebelle/about?//produ... - which is designed to more simulate real physical paint, not just in terms of brush patterns but also mixing.

Photoshop has an old, strong brand, allthe name is a bit anachronistic, but it has grown to be a product for all 2D visual art.

Edit: I see Rebelle is quite a bit like Paint. Shame they tell fibs about being “first” to emulate physical colour mixing. Alas, not iPadOS.