I generally like go and also see its problems as the author does.
However, with respect to the points about Go as a prototyping/starter language, there is not better language to start writing a project with in my opinion. Lots of languages have big communities of packages of various levels of maintenance but almost no other language has a standard library that is as usable as Go with the same guarantees between versions. I think its the biggest downfall of all these new languages like Rust/Zig/Hare etc, they all go for these minuscule standard libraries. I have no wish to start a project with any of them as all of them would involve I hunt down the 'best' http library and the 'best' async library and weigh their upsides and downsides, so I just reach for go and crack out the code I need to get it done, nothing else lets me do that half as easily, maintenance may be harder but at least I'm probably going to spend less time maintaining the list of packages that are still usable.
I dont know them as well as I do Go but the libraries (java especially) don't feel as coherent as the go libraries do, though that may be subjective and to do with my lack of experience with them. In addition both of these languages are large enough and have projects structured in such a way as to make it difficult to just use a text editor, which i consider a barrier to me just 'cracking out' a project.
C# also had pretty middling linux support the last time i worked with dotnet. and java tooling is not as out of the box as go is where I have to know is gradle good or still used or should i just use maven. Its all part of me not wanting to have to choose the best dependencies for my project and being handed for the most part good enough dependencies by the language standard library.
Another thing to appreciate in go is it produces good enough binaries and produces them very very quickly -- i've worked on several massive go projects and the build/test turnaround time is quite good.
With Go you can develop a web service with few to no external deps or frameworks, compile it into a single, static binary and then deploy it in a minimal distroless container.
With Java and C# there's a lot of other fuss involved with figuring out deployment. The code, build, test cycle is also much slower in C#/.NET ime. That's starting to improve a bit with the newer dotnet, but still feels behind other everything but the kitchen sink frameworks like Rails, which I would more compare C# to since C# without .NET/dotnet is uncommon.
Sorry if it was unclear, I was specifically commenting about C# with regards to build, test, deploy cycle because I don't have much experience with Java. It's good to hear that it's not slow or cumbersome.
However, with respect to the points about Go as a prototyping/starter language, there is not better language to start writing a project with in my opinion. Lots of languages have big communities of packages of various levels of maintenance but almost no other language has a standard library that is as usable as Go with the same guarantees between versions. I think its the biggest downfall of all these new languages like Rust/Zig/Hare etc, they all go for these minuscule standard libraries. I have no wish to start a project with any of them as all of them would involve I hunt down the 'best' http library and the 'best' async library and weigh their upsides and downsides, so I just reach for go and crack out the code I need to get it done, nothing else lets me do that half as easily, maintenance may be harder but at least I'm probably going to spend less time maintaining the list of packages that are still usable.