One concern is that if an EU company becomes very successful, it could easily be acquired by a large U.S. corporation.

If you have a good path and a bad path that may or may not converge sometime later on your journey, you still should walk the good path.

You're not wrong. But no SaaS is forever. Price rises, bankruptcies, ToS changes, change of CEO etc. Being acquired by a US company is just one of the things that can happen.

For someone like the author, it's not a reason to stay with a US company

And helping European companies be more successful might prevent them from selling out...

Don't worry, EU companies never become that successful