I agree with all of that, but honestly the more important factor is this is just not a very good cause to get all worked up about. Reddit is trying to grow into a profitable company, their business model is showing ads to users, they obviously can't just let millions of people use 3rd party apps for free.
I think even casual users understand this perfectly well. They don't use 3rd party apps for browsing Facebook, Instagram, Twitter, or Tiktok (because those services also don't offer APIs). Why should Reddit be different?
Reddit is different because it has been different. Not everything needs to conform prior social media models.
I think the cause is totally fine. I think framing it as some social justice cause is incorrect though. People really liked a thing and now reddit is taking it away in the name of money. The most downvoted post of all time on reddit is an EA post responding to monetization concerns in a star wars game. Seems right in line to me.
I think even casual users understand this perfectly well. They don't use 3rd party apps for browsing Facebook, Instagram, Twitter, or Tiktok (because those services also don't offer APIs). Why should Reddit be different?