Note that this whole twitter thread is in reference to Casey lodging an issue on GitHub about how slow Windows Terminal is, wherein he was told that his simple suggestion for making it fast would be a PhD level thesis worth of work. He was being polite and explaining things to them until then, but after that statement he was so disgusted he closed the issue and created refterm to prove his concept[0]. Then a bunch of people came out of the woodwork to make excuses for why it still couldn't be done. It's a fucking terminal emulator, a piece of 80s technology[1] that mimics a 60s technology, running in 2021, and people still think it makes any sense at all that it could be slow!?
[0] which is not anything groundbreaking, it's pretty much the obvious way to do things. He has intentionally done no optimization since it's designed to serve as a minimum performance benchmark.
[1] I'm guessing here, since I can't readily find an answer to when the first terminal emulator was released.