Photoshop is a good example -- not that I agree with everything in the app, but just to design all the interactions properly in photoshop would take hundreds of hours (not to mention testing and figuring out the edges). If your goal is a 1-to-1 clone why not use Krita or photoshop? With LLM you'll get "mostly there" with many many hours of work, and lots of sharp edges. If all you need is paint bucket, basic brush / pencil, and save/load, ok maybe you can one-shot it in a few hours... or just use paint / aesprite...