Obviously, those were highly competent engineers, but perhaps Elon Musk is just trying to get to roughly the same proportion (~60?).
If so, he's still got a long, long way to go, so expect a lot more cutting.
The founders controlled the small set of features available, and weren't beholden to, say, trying to include targeted ads or adding shopping to the platform. They certainly weren't concerned about bots, child pornography, state sponsored actors, data warehouses to store and analyze data for FCC decrees, the list goes on.
It's very easy, looking in, to handwave away complexity that creeps into a business and its technology and assume it's a lack of engineering skill. Do a reality check: Compare Twitter to other similar companies e.g. Facebook, Spotify, Netflix, Bytedance, Snap ... are these companies ran by 6 10x engineers? 60? Do you think EVERYONE is stupid or is unaware of how to do software engineering or is there complexity here you may be ignorant of? It's obvious Elon thinks the former here.
The more features you offer, the more complex your system needs to be, the more people you need to maintain and build on top of the system.