As another poster mentioned, it requires very little technical staff to just keep the lights on if you're not doing anything to move the business forward.
How many employees are “not necessary” depends on your priorities. If you mostly want to keep a site up and running, the requirements are relatively slim. Musk also laid off a large part of the Trust and Safety team, who don’t have much to do with keeping the site running technically but were responsible for moderation. Whether their jobs were “not necessary” depends on your assessment of how much moderation Twitter needs.
That said, yeah, I agree that it sounded like most of Twitter was bullshit. Actually I'm confused why the OP said "let's not pretend like bullshit jobs are real". Twitter seems to be pretty clear evidence that they are.
(I happen to think they're everywhere and that this article is just terrible. but even worse than bullshit jobs are the bullshit grift economy. After all lots of tech does make money, by doing stupid misanthropic shit. It's bullshit, but not because it's unproductive: just because it's productive at making the world worse for everyone else. Different problem.)