Becoming a YouTuber is much more likely then being an astronaut ever was, so this may be a good thing.
[1] https://socialblade.com/youtube/top/500/mostsubscribed [2] https://en.wikipedia.org/wiki/List_of_space_travelers_by_nam...
https://socialblade.com/youtube/channel/UCZdQjaSoLjIzFnWsDQO...
SocialBlade estimates their earnings as being at a minimum $4k per month. But the range is up to $56k per month. They also have a patreon where they have almost 4k people donating at least $1 per video, although when they last had their donation amounts public the average was substantially higher. IIRC that was was close to $10k per video. At four videos a month, that's $40k per month. They also were basically given a $1M boat by a luxury boating company, and many of their videos are sponsored by Audible or Squarespace.
So, at least for this channel, $500k/y in revenue is a pretty conservative estimate, although I'd bet even money they make more than $1M per year. I think setting the bar of "famous and successful" at 10M subs is too high.
By comparison, a "software engineer that works for YouTube" might have total gross compensation of about $35K/month, and there are > 1000 of them. Both your off-ramps and your reach goals are better too: if you don't get to be a software engineer that works for YouTube, you could get roughly equivalent compensation at any FAANG, a little bit less (but still six figures) at another software company, or if you're lucky and brave, found the next Twitch and sell it for a billion dollars. Your earnings on YouTube fall off much more dramatically if you don't get to the 1M subscriber mark.
You're almost always better off going into the unglamorous profession that enables (and controls the purse strings to) the glamorous profession than going into the glamorous profession itself.
NOW, none of this should be taken as an endorsement of YouTuber as a viable career path for most people. You are, I think, correct that your expected value is much better if you pursue software engineering. Especially if you're not extremely attractive, multi-talented, adventurous, and highly risk-tolerant. It is also a lot of work to make these videos -- SLV had one video where they went over the actual process of making their videos, and it is a six day a week job. But I want to make sure we're being fair to the YouTuber lifestyle here. For the ones that make it, very decent or even insanely good money is possible -- more than most people realize.
It's no different than actors. Those who routinely get the biggest box office draw and make the most money are those that appeal to the widest audience that will part with their money to watch them. Being appealing to the widest audience doesn't just come from rolling out of bed and switching on your webcam. You're going to have to work for it just like actors do... harder in fact, because you've got far more competition on YouTube than actors have at the box office.
If you want >10M subscribers, you've gotta provide more value than the average YouTuber.