I think Elon has accomplished a lot, but I think you're ignoring the fact that every one of his companies is still surprisingly risky. Tesla might not get another loan and it could go under in a year. SpaceX has fantastic margins, but they still have significant hurdles with failed launches (although this is true of rocketry in general) and navigating a political landscape. Solar City was going under when Elon saved it by combining it with Tesla, a very controversial move.
Elon has yet to run a profitable electronic vehicle company. Elon has yet to run a stable alternative to NASA. Elon has yet to ween the world off its oil dependence. He is working towards all of them and it's great! But he hasn't succeeded in disrupting any of them yet, because all of the alternatives still exist and are as healthy as ever.
An alternative to NASA is an odd and incorrect way of describing SpaceX. NASA is a customer to SpaceX, there is no intention of being a NASA alternative. You could say they want to be an alternative/competitor to the aerospace and defense contractors though
Sure. Alistair Pilkington and Arthur Fowle, between the two of them invented the technologies used to create almost all glass. It might not seem like it's high impact, but from the glass in office buildings, to automotive glass, to smartphone/tablet/TV glass, two highly impactful people who touched more than Elon Musk has.
Allan Alcorn invented Pong. It spawned and inspired an industry that grew to almost $100 billion, and the technologies used in video games have spread, again, to every aspect of technology, to the point that Microsoft used Cortana, a video game character, to leverage name/brand recognition with gamers in one if it's core products.
Bill Gates, for better or worse, transformed the personal computing industry, and has been on a humanitarian campaign for the last several years.
Setting aside food supply management politics, Robert Fraley introduced the first work on transgenic foods and continues to be a strong contributor to modern food science.
Norman Borlaug. "and is credited with saving over a billion people worldwide from starvation" is the best introduction a human could have. If you don't know who he is or what he did, you owe it to yourself to learn more :)
Moving on to relative contemporaries:
Linus Torvalds made Linux, which as you may have heard, has impacted technology a bit.
Tim Berners-Lee and Robert Cailliau basically invented the web and inspired the modern web.
On the tech and financial side, Mark Zuckerberg has done quite well with Facebook, and for better or worse is driving connectivity into unconnected parts of the world.
Elon Musk is a visionary, and is pretty cool, but he is not exactly once-in-a-generation.
I literally laughed out loud at this. Obviously greatness is subjective, but you are really reaching if you think someone saving a billion lives isn't 'on the same level' as Elon Musk who has yet to go to the moon (although I'm sure he will), who has yet to make a profitable car company (this one I'm not so sure about), who has yet to change the energy infrastructure of the world (he's chipping away at this one steadily).
The important thing about history is it's written after the fact. If Elon Musk died today he would be remembered for his work at PayPal and starting several ambitious companies before they achieved financial success. I'd wager that if he died today all of his companies would fail and he would be remembered for trying to do too much and working himself to death before he achieved his goals. He could very well end up as a Greek tragedy.
You are just reinforcing my point. You're listing people that are generations in the past, which is exactly what I said. you're grouping Elon into a once-a-generation / once-a-century type of person.
Elon has yet to run a profitable electronic vehicle company. Elon has yet to run a stable alternative to NASA. Elon has yet to ween the world off its oil dependence. He is working towards all of them and it's great! But he hasn't succeeded in disrupting any of them yet, because all of the alternatives still exist and are as healthy as ever.