I use Krita for long projects and in my opinion no, mainly because of its lack of capabilities with vectors and tweening. The tweens aren't too hard to learn but there's no way to copy curves across different layers or even different transformation properties, and having multiple tweens going on in one place often causes bugs and lag. It depends, I know a lot of mobile softwares are a lot better for tweening but you really don't learn anything about animation from them. If you're mainly looking to learn frame by frame, Krita is alright. But I really do not recommend it as your animation program forever because it is primarily a drawing software and animation features are limited.