Inkscape: Completely capable. I know many people who have used it instead of illustrator professionally for years.
GIMP: Depends on you. As someone who learned GIMP long before ever learning Photoshop, I find Photoshop unintuitive and frankly stupid. So it’s all about what you learned on. But GIMP relies on spending a few minutes setting it up for your own use case. Literally every window can be moved to anywhere. You can have whatever windows you want open all the time, or hidden behind right clicks, etc… Your tabs and tab groups are completely customizable to how you want to work. BUT the rub is that you have to be interested in doing that. GIMP is trashed for having a bad default UI because the expectation is that it doesn’t have a default UI. My GIMP would look entirely different from someone elses because I use different tools that I want front and centre than someone else might. If you’re not interested in that and just want something that you can learn a “default” setup and go with it (and there is absolutely nothing wrong with that) than you’re better off sticking with Photoshop.
As for Krita, whatever else people are telling you, Krita is NOT a replacement for GIMP if you’re doing design work. What it brings to the table in terms of having built in Vector capabilities it negates by having a very limited and basic suite of selection tools. Something that would take you two seconds in PS or Gimp to band select, paint the foreground, feather the selection, shrink it, etc… takes five extra steps in Krita because Krita is a drawing program not a graphic design program; what few “advanced” selection tools they’ve introduced is tacked on and hidden between three or four extra steps because it just wasn’t designed to have them at first and they were added later.
Just because it looks nicer out of the box than Gimp, doesn’t make it better. I’ve tried replacing Gimp with Krita because i like the KDE suite of apps in general. But I was pulling my hair out trying to do even a basic composition using it’s archaic selection tools.
I would agree with that. But in all of their defence I’d add that they’re not trying to be. They are their own pieces of kit with their own roadmaps and goals.
The biggest frustration people from Photoshop have is that the expect Gimp or Krita to be a clone of Photoshop with feature to feature parity, and that’s never been the goal of either program.
Photoshop has spent decades basically merging the features of most of their products, so that it’s now basically a photo editor with features of Illustrator and a suite of advanced drawing tools. The only replacement for that would be a hypothetical program that combines Gimp, Krita & Inkscape. But that’s never been the goal of any of those programs. They’re separate kit and as far as I’m aware always will be.