The problem is people think of this in terms of "cost to keep the server on that serves an API request" and not the opportunity cost for ad engagement that actually makes the business viable.
This is what people said about third-party Twitter apps, yet all of those power users and brands are still there, except the ones who are ideologically opposed to Elon (and were leaving anyway). It doesn't really seem to have made a difference.
Twitter is worth around a third of what Elon paid for it. I'm assuming you're happy to just assert that 2/3 of it's lost value is just those "who were leaving anyway" and changes like those to third party apps had no impact?