I completely agree with you on this. I was considering GIMP as the only relevant substitute for Adobe until I've played a bit with Krita. Really amazing piece of work.

To be fair, GIMP considers itself also an image processing software, not (or only partially) a painting program. At least, it emphasizes this aspect and it shows (yes it mentions also artistic usage).

I'm using it this way as a tool (being a software writer in this industry), but the tasks belonging to it and those for Krita have a virtually empty intersection.

You're absolutely correct, but you know how these things go: people look up FOSS Photoshop (or more likely "free photoshop alternative") on a search engine and GIMP is the first hit and when the tools for drawing aren't as sophisticated, users will say "GIMP sux" because it doesn't match their expectations if they're a drawer even if it's a perfectly adequate image processor.

Rebelle is also quite nice. They even have an HSLuv based color picker. Super underrated software only a handful of digital painting pros know about ;)

https://www.escapemotions.com/products/rebelle/index.php

Clip Studio Paint and Affinity are also well-regarded, though not FOSS. CSP in particular has great support and advanced tools like posable maquettes and perspective rulers.

While we (Krita) don't have 3D support yet, but we do have perspective and other kinds of rulers (assistants) support. There are lots of other features too like wrap around mode for seamless tile creation etc.

For the record, I have all 3 installed. :) I find that they're useful for different purposes and that it's helpful to be able to tap into two feature sets and support communities.