One point OP may have missed is learning opportunity. The opportunity to learn in a big company, any big company is simply not the same as that in a startup. You are always one of 50 people working on a feature that has already been spec'd out in great detail by some one else. Early in your career investing in learning and becoming a better engineer makes a lot of sense.
Even as an intern at Google many many years ago, I was one of just a handful of engineers working on a feature, and even though my internship lasted only a few months, I not only had a considerable part in the feature's implementation, I was also given plenty of opportunity to give my own input.
Now, many years later at a different large company, that has not changed. The total amount of people working on a significant feature may be large, but that's mostly when the feature is very cross-functional, and well, just generally large. Most teams we interact with still have the size of a handful of people, and they very much have the authority and responsibility over their components.
Obviously there are a lot of factors in play, and I don't at all doubt that jobs like you describe exist (though 50 people with no spec input still seems like a vast exaggeration to me), but I highly resist the claim that working in a big corp means that you're bound to be a small cog in engineering. Quite the opposite: It can be a large lever giving you the opportunity to work on things of amazing scale and effect, that a startup simply does not have the resources for.