With time, reading, discussion, reflection, practice, and experimentation you can integrate into a team and grow to understand how things are, then why they are, then how that's working out, and finally how they can be improved. This process takes months, even years.
It's very unlikely that an outsider could be shown a random diff on a random component in a Twitter-sized architecture & even know what it's doing or why, let alone make a reasonable judgement on whether it's a good idea or the best way.
I’ve been coding for 39 years. I know how the process works. And yes, it does take time to get the deep understanding of any system. But it is not on the scale of impossible for a squad of 10x engineers to answer and/or develop some basic questions in a short time frame. And much more reliable than trusting the existing crew who has been quite publicly represented by persons hostile to their new boss. I do not in any way mean to cast ALL engineers at Twitter in this light. But it is quite clear the bullies there have grown quite accustomed to their pulpit.
Which parts are unnecessary and which people should be fired, is not one of the basic questions for which you're going to get a good answer in a short timeframe. Now it's clear that there's a lot of animosity for Twitter in this thread - maybe people don't particularly care of the decisions made in this process are correct or just because they all had it coming anyway - but imagine someone doing this to your shop. Come on. It's ridiculous. You'd be pissed.
Your scope of investigation is much larger than the one I stated. One thing neither you or I know at this point, was it a 2 hour visit or is it one of Musk’s marathon “pull up the couches cuz we ain’t going home till we figure this out” sessions.
It's very unlikely that an outsider could be shown a random diff on a random component in a Twitter-sized architecture & even know what it's doing or why, let alone make a reasonable judgement on whether it's a good idea or the best way.