Thanks for the answers, but that one in the video pretty much just bakes it without doing anything fancy.
I tried using that basic approach for my oil drum again and than tried replicating that with a regular square. Interestingly in both cases the result seemed not to be pretty. And I still have no idea what I did wrong. Maybe I should try presenting my problem at some specialized blender forum.
Than again, I always end up getting problems that no one else seems to get in pretty much anything I attempt to do.
I also tried using XNormal because many people seem to love it, but the result seems to be even worse.
(This here are two oil barrels in unity with normals from blender and xnormal respectively)
try exporting model to unity or unreal, its easier than blender rendering
also lowpoly version looks like it already has a lot of detail
The thing is that I'm trying to go for a look as realistic as possible (not in the sense of trying to achieve photorealism, that would far out of my reach, but in order to try going for a look good enough so that its going to work for a gritty horror game). Once I somehow manage to set up a test scene with self-created assets in unity and figure out a workflow, I'll go back to blender and try giving it some dents with sculpting, so it looks old and rusty.