A person can both be very good at something but also completely useless to the company as company priorities/needs change.

I'm frankly not sure why Twitter needs to own an entire design agency (presumably they've acquired all the staff) especially in 2021 when their design was already set in stone and hasn't changed significantly since then (so indeed, what has this guy been doing?).

Now, I'm not defending Musk here and especially not this childish reaction - he should be following the accepted protocol for making employees redundant instead of cutting them off and laughing at them publicly on social media.