I don't really understand this type of criticism. People complained that Go didn't have generics, and now that they've delivered, people still want to complain for some reason.
I can quite believe that the Go team wanted to be sure that the approach made sense for Go, that it was the right solution to the right problem and to keep to their backward compatibility promise. Experience is a good teacher. I really don't know why it matters in the slightest that they didn't arrive at that on day one.
>they spend a decade insisting that they right and everyone else was wrong
This just isn't how it happened. The Go team never said that they were opposed to generics. Their stance was (i) that it was not a top priority and (ii) that it was difficult problem and they'd take the time to implement generics correctly.
The idea that this is about one group of people finally proving that they're 'right' is a distortion based on viewing events though the lens of snarky comments on the internet.
Generics aren't a cutting edge feature that they wanted to see how it would develop. Their objection against it was ideological.