This is just not correct. It runs on a protocol - anyone can create software that uses the same protocol and communicate with Bluesky users as equals.

Were they right to develop their own protocol rather than to improve upon AP? Probably not. Is ATproto completely dominated by Bluesky? Yes. But is not like Twitter.

I can - and do - communicate both ways with Bluesky users through Mastodon and Bridgy Fed. That would simply not be possible with Twitter.