As an experienced user I’m extremely happy about the review and approval process – thanks in passing to the opam repository maintainters for the unglamorous work they do on it. It takes time but it doesn’t just slows things down it’s an excellent QA and usage signalling tool.
For example for the cmdliner 2.0 release which was an exceptional breaking release, the centralized repository allowed me to pretest the release and warn each package that was going to be broken by that release. The opam repository is also routinely used by upstream to test some changes to see if some syntactic quirks are present in the wild.
Besides it also shows me how my packages behave on platforms I wouldn’t personally take the time to test on.
If everyone publishes their package in their corner all that is lost. We no longer have a large corpus of language and package usage to inform some breaking decisions.
Note that while the process is currently managed on github. There is nothing in it that depends on github. AFAIK there not is a single line of code in the basic mechanics of opam that relies on github.
If you want to live disconnected from the eco-system you can always publish your own package repository.