As far as (1) goes, 90% of the content on Lemmy is just a Lemmy circlejerk, the remaining 10% is memes. What influx of “low effort content” could possibly make the discussions on Lemmy worse than they already are?
As far as (2) goes, you realize your data on Lemmy is open to everyone to scrape, not just Meta? Every single one of your upvotes is public.
This is where your argument falls apart. Why? There is no incentive for instance mods to want to grow their instances exponentially.
If Facebook’s ActivityPub grows to be incompatible with the existing implementation, who cares? So what if you run a Mastodon instance and aren’t getting millions of new users a day?
This is much ado about nothing. While there is a shared platform, enjoy the ride, and if they don’t want to play by your rules anymore, there’s no harm to anyone in saying goodbye and staying your course.