Welds on the painted railing - assessment?

never ever!
Look closely to the left and right where it all begins...
Also, the lower and upper "fraying" fit together exactly
I am sure it is sharp-edged when you run your hand over it

I am sure that it is sharp-edged when you run your hand over it

Exactly. I have enlarged it for the unbelievers:

I don’t know where you see paint chips here?!
In the second picture, I see a torn edge! Nothing can be repaired here.

Can you explain to me, as a layman who has no idea which work steps are required to manufacture such a railing, what would now be necessary to get a decent railing? Or rather, what problems should I expect if he tries to touch it up with his paint pen? Will only the appearance suffer, or also the durability against weather damage?

To me, your explanation also sounds like the damage did not occur during the installation, but already before the powder coating was applied.

In my opinion, you can't save anything there anymore. Especially not with a paint pen. Actually, the photo should be enough to claim it as a defect with the manufacturer. They should be able to recognize it just from the photo. From my layman's perspective, it shouldn't affect the durability. It just looks ugly and you can hurt yourself on it. I would insist that the element be replaced. You can see from the dent on the far right that this damage must have occurred before powder coating.

By the way, you already have deep scratches in the coating on the handrail!

Can you explain to me as a layman, who has no idea which work steps are needed to manufacture such a railing, what would be necessary now to get a decent railing.

Maybe you should simply read the thread carefully, everything has been said (several times).

To me, your explanation also sounds like the damage did not occur during assembly, but already before the powder coating was applied.

Definitely yes. You failed to have the weld seam cleaned up by grinding and polishing yourself and thus also ensured that welding wire splatters adhered to the material and were coated.

Or which problems should I expect if he wants to touch it up with his paint pen? Will only the appearance suffer or also the durability against weather damage?

You cannot "fix" this by simply applying more paint surplus!
I don't understand you: You are the OP and don’t have to misinterpret photos like the other discussants, but can get so close to the object live that you can determine the difference between adhesion and an alleged scratch. That is after all the opposite and at least can be recognized by touch if you already confuse it visually. The durability suffers because the material at the contact points with the welding wire spatter has not been galvanized before it was coated. More than touching it up "optically" is no longer (meaningfully) possible: I would have the welding wire spatter burr carefully cut off, and as a further treatment a paint pen would suffice for me. You won't fix your whole stinginess damage anymore anyway – except by an absolutely disproportionate and pointless full replacement (your responsibility and no one else’s). The welder did a proper job (correctly, you don’t get what you haven’t paid for), and the coater coated (not nicely, but correctly) what was delivered to him. Normal stinginess consequences, next time you can be smarter.

Actually, the photo should suffice to complain to the manufacturer as a defect. He must already recognize that from the photo alone.

It’s easier to misconstrue from the photo, but the expert on site is not fooled by that.