This is a PR statement that has been introduced only after Go generics landed, for years generics were dubbed “unnecessary complexity” in user code (Go has had generics from the beginning but only for internal use of the standard library).
> Go has gone on to be very successful in cloud and networked applications (which it was designed to cater for), which lends credit to the practicalities of what the designers thought as important
Well, given that the k8s team inside Google developed their own Go dialect with pre-processing to get access to generics, it seems that its limitations proved harmful enough.
The main reason why Go has been successful in back-end code is the same as the reason why any given language thrive in certain environments: it's a social phenomenon. Node.js has been even more successful despite JavaScript being a far from perfect language (especially in the ES 5 era where Node was born), which shows that you cannot credit success to particular qualities of the language.
I have nothing against Go, it's a tool that does its job fairly well and has very interesting qualities (fast compile time, self-contained binaries, decent performance out of the box), but the religious worship of “simplicity” is really annoying. Especially so when it comes in a discussion about error handling, where Go is by far the language which makes it the most painful because it lacks the syntactic sugar that would make the error as return value bearable (in fact the Go team was in favor of adding it roughly at the same time as generics, but the “simplicity at all cost” religion they had fostered among their users turned back against them and they had to cancel it…).