I had a coworker at a big tech co (where we wrote primarily Java) who used VIM, without any extensions to make it easier with Java, and he wrote all his import declarations by hand. Maybe knowing exactly which sub-namespace you're pulling Java utils from is important. I'm willing to bet big that it's not.

I'd say not important, but in a way important to be able to do it without, just in case.

Think of old Borland "IDEs", people used to code in only yellow text with no syntax highlighting. Sometimes the slowing down is beneficial.

Sure, having completion and tree sitter highlighting is a very comfy thing to have, but sometimes not having them is a nice exercise.