Heating pipe bent too much?

Been there, done that. So not that bad, but annoying with craftsmen. It's not nice - but also not the end of the world. The mere fact that they agreed to improve it actually shows that they don't completely not care about the whole thing. If I were you, I would call in an expert to support you in such matters - it's still a shell construction and surely you can still see a lot and ease your conscience a bit.

I decided against an expert back then because I thought building with an architect would make life much easier, but the guy is at the house maybe once a week if at all, I have discovered all defects, really ALL, and forwarded them to the architect, sometimes I wonder what I'm even paying him for

Fully according to HOAI? Then call him to duty and summon him to the construction site!

I already did, I sent him a fat email back then saying that it is not my task to spend hours on the construction site every day and find defects, since then it has improved a bit, I have also not paid the partial payment for 3 weeks, this will not change.

oh, it is a shell construction and you can probably still see a lot and calm your conscience a bit.

You can’t see anything anymore - it surely must have already been plastered. For an expert, it is (actually) too late - at such points they tend to make things worse.

Have you also commissioned the corresponding service phase? My architect hasn’t been there since the roof/windows installation either - he didn’t consider it necessary anymore.

You're right - it's already plastered then.