If you need more than a microservice, then you need more than Go in my opinion, and C# is an excellent choice. I think most of these startups going mono-lingual on Go are going to regret it, just like the startups that went mono-lingual on Node.js a decade ago.
If you're building anything that requires some serious architectural structure, and that might be easiest to implement as a monolithic app, then you need a language that supports that instead of getting in the way. Now with Typescript Node.JS might finally be suitable. But I'd definitely consider Ruby and C# or maybe Java or even Haskell first. Maybe Elixir, I heard that's still going strong as well.
You didn't mention which tooling you miss.
Neither did you.
What do you find missing from the Java tooling world? In my experience it’s been the best built out, and maybe overly so.
Note: not trying to pick a fight, I'm legit interested what I might be missing since I feel like my needs are pretty much covered :)
Historically though (pre-.NET Core), .NET was always in a Microsoft bubble which held it back as the industry consolidated on Linux and Docker. The person you're replying to may agree that C# tooling is currently pretty good.
I cannot, however, compare it to modern Java or C#.