I wouldn't say something lacking a LSP is modern by todays standards, as that would mean it lacks syntax highlighting, go-to definition, and other basic things for a bunch of languages.
It isn't good enough. There's a bunch of new languages coming out all the time, and even ones that are 10 years old (Clojure) aren't supported well in editors without LSP support, like Micro. LSP support allows the language ecosystem to provide the building blocks so that developers could write that in any editor that supports LSP.
I have never found the need to use go-to definition, until I started working on some golang codebases. The code organization in these codebases is typically abysmal, with multiple files in the same package participating in N ways nested orgy.
Of course, micro is written in golang, and it seems like the author is doing just fine without relying on LSP.
If you've never needed to use go-to definition then I assume you never work on anything even remotely large. But even in projects with, I don't know, 10 files, I find go-to extremely useful.
