I think they are. The biggest threat these companies face is not needing them. Hence the bullshit google is trying to pull around their browser. When they make dumb decisions they empower alternatives. The fediverse wouldn't be where it is right now (which is an amazing growth cycle) without these companies making dumb, self deprecating, shitty decisions. It may not be obvious, but the fediverse is something altogether different than what has come before, and empowering it even a little bit is a serious existential threat to these companies, because it represents a true, unsquashable challenge to their power structures. The fediverse represents a return to the spirit of web 1.0, with the niceties of web 2.0-3.0. I kind of hate the 'Web X.0' framing in this sense, because these things are happening concurrently.

The web 4.0 these companies are, as a cabal, trying to build is a walled garden with you as a victim to as much shit as they want to shove down your throat. The fediverse, its growth, and more importantly, its philosophical structure of open source, open access, and consent represents a kind of impurity in their walled garden that means they'll never truly be successful. Lemmy doesn't have to kill reddit. It just needs to not be killed by reddit and continue to be viable.

There may be a hard fork coming to the internet. I can see a future where open access, anonymous and private resources depart from the internet of corporations, tracking, and identity as product. With out the fediverse that wouldn't be happening (crypto sure as shit wasn't gonna get us there).

So yes, even if these companies aren't feeling particularly threatened at the moment (and I think some of them recognize the threat. I think Zuck sees it, hence threads), there is a true existential threat facing them. Its the world not needing them quite as much as they once did. It may not seem like much, but that is a huge threat to companies who are locked in a growth or die system. The fediverse on the other hand, doesn't suffer from a 'growth or die' meta-paradigm. It can grow slowly. It can have patience.