Poor painting work or poorly plastered?

Yes, it works. So at least every reasonable painter should still be able to manage that now. Unless he knows that his paint is really bad and that he can't (or doesn't want to) sand it down and that nothing else will adhere to it. But yeah, for a thousand he won't do it even without bad paint.

I have problems with the evaluation of the plaster since the quality of the photos is not the best. They are phone photos, and the phone software does quite a bit itself. What I see has little in common with our own Q2 plaster. Q2 is also fine-grained! What I see here is more like our exterior plaster structure, which is coarser-grained. Additionally, it looks like the painter used too little paint. As already said: what can be seen in the photos here may possibly not correspond to reality.

Exactly that! What kind of plaster did the plasterer use? That looks like roughcast.

Beyond that, I see the "mistake" with the painter. Even as a "professional," he has some obligation to inform the layperson that you shouldn't just paint over such a surface.
But who knows what kind of "professional" was at work there. The OP can surely say more about it - if he wants to.