You're getting downvoted for this, but factually what you're saying is correct. He did lay of 90% of the staff and although people have claimed Twitter will die any minute, it hasn't.

Whether or not a lean team is the way to go perhaps remains to be seen, but what I'd say is that my anecdotal opinion on this is that the majority of engineers are a liability and assuming that 10x more engineers means 10x more work done is incorrect. Most engineers can build stuff, but they also add complexity and require hand holding. Both suck time from the most productive engineers.

A team of 10 excellent engineers is easily better than a team of 100 good engineers, in my opinion.