Why not? I think his reasoning makes sense. Unless you mean that having a language with better design (but being released later) is not an improvement.

My argument is that timing is very important to adoption. Unix is not the best OS to have been designed by far, but it was the first free one. If go had been delayed, something else may have filled the slot, and there’s no reason to believe it would have been a better something else. I.e when Go did release 2 years later, but with generics, it’d be too late, and no one would care.

I'm not sure the creators of Unix would have agreed. Unix was a step in a very different direction at the time. It was a reaction to baroque operating systems that did a lot of stuff and were quite complex. The key to Unix is simplicity and, if you shave it down, that it was really a system interface definition - which enabled other people to create Unixen by offering the same system call interface with the same semantics.

It was neither free, nor do I think the timing played much of a role since there wasn't any comparable OS being made at the time. The important bit of Unix was a set of key ideas.