There's a few claims made here:

Autonomy/impact/influence. This is maybe true, depending on things. My manager^4 knows who I am. As does my manager^5. I've interacted personally with both of them. I've openly criticized both of them. I've openly criticized other VPs. It's possible that I'm on someone's shitlist, though at this point I doubt it.

In term of impact and autonomy, I set most of my own goals at the 6 month and 1 year scope, and have influence with my leadership on defining our long term initiatives. I have the autonomy to work on a pie in the sky project that takes up 30-40% of my time that has no chance of being valuable for months, and only a potential for being useful at all. I came up with this, from the ground up, myself.

I think I've had an above average experience. But the idea that everything interesting is already taken isn't true. The idea that nepotism runs rampant also isn't particularly true. One thing I'll note about larger corps, especially G and FB, is that managers get more training on how to be managers than at most other companies, this means that they'll encourage you to set career goals, and work with you on figuring out how those can happen. This can include helping you move to other teams. Again this isn't universal, bad managers exist, but I'd hypothesize that the median manager at FAANG is less shitty than the median manager at a smaller but still billion dollar company.

The H1B abuse stuff applies, as far as I know, significantly less to FAANG than other tech companies. If you include contractors/vendors this can get murky though.

I don't disagree about HR not being particularly friendly at megacorps. But you're not going to have a particularly better experience at a smaller company. If you antagonize a smaller company, it may still end badly (and I'd argue there's a higher likelyhood something you do will get taken personally).

Arguments about gig workers and unethical behavior by the company apply as much, if not more, to smaller companies like Uber and Lyft (and Doordash and and and). And ultimately reduces to a sibling of the "no ethical consumption under capitalism" argument. We certainly shouldn't throw up our hands about such things, but if you try to self-host your server, you're still purchasing components that probably involved dangerous cobalt mining and there's a good chance that you'll be using more energy than if you ran in a datacenter in the cloud.

There are indeed many other companies. But that doesn't mean that small companies are better. Is Uber-under-Kalanick more ethical than Amazon? Is Uber-today more ethical than Google? Is Square more ethical than Microsoft? Sure, maybe, but I don't think the answer is so blatantly obvious that these conclusions can be drawn so strongly and with so little nuance.

The core argument here seems to be that since big companies are large, and they do bad things, they're somehow worse than average because they are big. I'm at least somewhat receptive to these arguments, since things like monopoly concerns come into play at some size, but trying to blame individual employees for choosing what is ultimately a much better deal for them when the problem is that the company is (maybe) too large isn't a great approach.

Heck, for a particular ethical individual, the concrete ethical impact one could have by working at a FAANG as opposed to a smaller company is probably larger, you're betting on the influence you'll have in the small company being comparatively greater than the influence the small company has compared to the big one. Maybe that's true, maybe it's not though.

And the whole time, the big companies are on average treating employees better than small ones.