The problem is not mvcc but postgres’ implementation details of it.

In what way? I didn't see anything obviously improper when I learned how serialization isolation worked.

A delicated full vacuum process that need full locking, how little isolation between tables, etc

Lots of the pain point have been mitigated in the last ten years. It is now as simple as other comparable complex db can go (i.e. Not simple, but you can't find better product)

TFA covers its issues? It’s specifically compares postgres’ to other implementations’ (oracle and mysql).

Also the paper linked from TFA goes into the various implementation options in more detail: https://db.cs.cmu.edu/papers/2017/p781-wu.pdf