What about founding a startup to try to make big money and then have the time to explore things?
It takes way too long for the average startup to be successful, and the overwhelming majority of them aren't successful enough to provide the economic freedom you are referring to.
If you can love the chase of a startup, and love the thrill and long hours, great!
If you are doing it so you can have "more free time later" there are many many better strategies.
Then when you're sick of it, move to a cheaper area, get a part-time job and sell 3-4% of your assets every year to make up for the deficit. If you're lucky, the safe withdrawal rate of 3-4% will even be enough (or close) to have the ability to quit working for a living completely. Or perhaps your part-time job can cover all your expenses and you can just keep letting your portfolio grow at the expected long-term rate of 6-7% per year.
But obviously, your total spending will increase, so you either have to earn more after having kids or save up more before having kids. If you want to raise your children in a high cost-of-living area, this will of course be even more pronounced.
Then you've lost three years of your life and have to go somewhere else.
Sure, you gain knowledge and experience through that time, but joining another company would still take time to work your way through the ranks there. In that three years, you would've had a great head-start on both professional experience and financial health.
Food for thought. Your statement just assumes the startup will do well and that's not a guarantee. There isn't a guarantee a company you work for will be around forever either, but the likelihood is far greater.
2) even lower probability if you're an opportunist as described (note that smart investors like YC actively avoid them).
3) large minimum years investment required, especially if acquired or acqui-hired, maybe 4-10 years, during which you suffer the opportunity costs I described.
4) just easier to explore and be open to the rare opportunities, while still making decent money, by doing something like consulting at low hours. From this position you can always do a startup if you see something great.