If these features were critical enough that you could found a company on them, then clearly they brought innovation to the scene. If they had not come along, it's unclear as to whether Facebook would have ever introduced those features in their products.

"Fair market competition" is the idea that products compete on their own merits, not that you can leverage your market position to destroy competitors. "Deeper pockets" is certainly antithetical to fair competition even if it's a reality we must sometimes accept. Exploiting the fact that you have "more users" should probably also be looked at as anti-competitive since it certainly doesn't benefit consumers by locking people into exclusive platforms.

Are we really going to resign ourselves to the idea that FAANG will now and forever own nearly all the internet? What good are the "principles" of "free market competition" if we allow consolidation to effectively eliminate the market?