as someone who has worked for these tech companies for 20+ years I'll just say LOLTwitter was horribly overstaffed. Most of these tech companies are. I think the platform is running fine. It hasn't had any issues for me. Maybe it will all collapse tomorrow, but I doubt it. My feeling is most of those engineers were doing about 20 minutes of work a day.
Time will tell if he can make it work, but I won't bet against him. He has made stuff work that no one thought was possible. The guy decided to figure out how to land a rocket after using it. Everyone told him he was crazy. He now does it constantly. We are so used to now if something goes wrong that's the story not that it went off without a hitch.
is there fat? Sure. Is it everywhere in every business unit and every tech company absolutely not.