How important are scholarly credentials vs just having that knowledge without a diploma?

I think in almost every field and occupation, having the scholarly credentials is extremely important. Knowledge without the credentials is pretty worthless (unless its worthwhile in itself, but even then you can't eat it): using that knowledge will generally require that people put trust in your having it, often when they're not in a position to evaluate how much you know (either because they're not experts, or they don't have the time). Credentials are generally therefore the basis of that trust. Since freelance work either requires more trust, or pays very badly and inconsistently, credentials are worth getting.

And that was the point of my previous post: some way or other, you have to earn people's trust that you can do a job worth paying you for. One way to earn that trust is to perform well despite lacking credentials. This will take an enormous amount of time and effort (during which you will not be paid, or at least not well) compared to doing whatever it takes to get as close to a 4.0 as you can. The faster you get people to trust you, the faster you can stop fighting to feed and shelter yourself and start fighting for the future of humanity.

Getting a degree sucks because it's expensive and time consuming. But if you work harder than everyone else around you, you'll get through it faster, and scholarships will make it closer to free. The whole point is just to get to a job where you're doing some real good as soon as you can. Getting solid credentials is without a doubt the fastest way to do this for almost everyone.

The exceptions are people who are either very smart or very lucky. Obviously you can't count on luck, but you shouldn't count on being a super-genius either. First, you're still in high school at 17. People smart enough to skip the normal system of credentials (which is really, really, really smart) are not in high school at 17. And the credential system is and has been tightening for decades, because higher education is so packed with people. You're going to be competing with people who have degrees at almost every level, and not just BA/S's. Empirically there's no question that they out-compete people without degrees.

Not every degree is worth getting, of course, but the 'autodidact' thing is almost certainly just going to be the longest and hardest path to getting where you want to be.

ETA: I don't remember the specifics, but EY once said that very probably every person-hour spent working toward FAI saves [insert shockingly large number] lives. Think about it this way: those people are all looking at you from the future, watching you to see what you do. You're looking back at them, and watching [insert shockingly large number] of them vanish with every hour wasted. Time is a factor.