While I agree that getting locked out is a clear risk of any business built against another company's platform I do think it is perfectly reasonable for someone whom has done so for 15+ years (and is part of an ecosystem that helped establish that third party) to be publicly upset for the mode and method for how this change happened at twitter. Its not just his frustrations being vented in this post but the impact to his users (which is well out of his control).
Twitter's actions of breaking the API for the largest 25 integrators with millions of users (by all indications) on purpose with 0 deprecation warning, 0 communication, 0 response the the break is garbage. Knowing that Musk is the agent of change and the one setting these actions in place he can take the heat.
at the end of the day I am done with twitter as it is, so its no skuff on my skin either way -- as far as I am concerned there is a clear path forward for the types of actions Musk has taken at twitter. It is just a matter of time.