Startups are not much risk, though. You start out without, you try to make something, if it doesn't work out just having the experience as long as it wasn't a total catastrophe makes you hirable anywhere you want or you try again.
The most you might lose is the support of friends and family if your dreams aren't fully realized. Which can be a lot, but that is why the people who have the most to lose don't try startups.
There is opportunity cost which is working for a big company from the start.
If startups are not risky enough to be irrational to get involved, are you saying then the big companies are acting irrationally when not getting involved?
That's of course a dual view. But it seems to me that the big corporation is more likely the one that calculates the correct expected ROI than the startup in the unknown space..
Of course not, it's hyperbole. Your criticism can be applied to anything [1], because nothing will make someone hireable everywhere.
The point is that if you go through a decent period [2] of running a start-up you will acquire experience and skills that will make you much more attractive for hire compared to yourself without that experience. What's more, the quality of this real world experience will most likely far surpass anything you would gain in a classic university in the same amount of time [3].
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[1] Depending on how literal we want to be with these word games, there are some tricks that can be done with the "you want" part of the phrase to adjust how much it applies.
[2] Let's say 6 months full-time minimum.
[3] There's no way to give a universal estimate here for everyone. However for people who are capable of self-teaching, the startup experience can be orders of magnitude more useful than university time.
The most you might lose is the support of friends and family if your dreams aren't fully realized. Which can be a lot, but that is why the people who have the most to lose don't try startups.