They often do have a "soft" feel even when absolutely focused. The "dohnuts" in specular highlights that are out of focus are odd to most.
There were a lot of "off brand" lenses made.
I have "heard" that Vivitar and Tamron made the better off branded ones.
I had the Nikkor 500 at my disposal for years... never reached for it much, and only remember a couple memorable images made with it.