Deliberately using an alternative is a form of protesting.

And it can be, sure, but it's not always the case.

I'm not just using Lemmy until or if Reddit backtracks, I'm using Lemmy because I believe it's the superior platform in many ways and has more to offer. I didn't make an account here in sign of protest, I made one because Lemmy was suggested to me and I'm liking it better than where I came from.

I'm also aware that many users on this platform would go back to Reddit if they backtracked on the API keys.

No. And it's specially not the case if you consider the "alternative" to be better.