I've gained a ton though random wanderings on the internet and wikipedia and so on but it's really not the same as reading one in depth work a person put 500+ hours of their life into.

Yeah, a book is researched, thoughtful and laying a long, and complicated argument. Just the act of reading the long forms of ideas will make you better at thinking.

Reading a Wikipedia page or watching a video, almost always dismisses the ideas that lead to a conclusion, which is what you need if you want to THINK, not walk around with containerized ideas that other people came up with.

But most books could be a 100th of the size they are

Indeed. There's a reason for that: Most modern non-fiction books are the result of a publisher giving a book deal to an author to expand an article they wrote and people who are going to spend $20 on a book want to feel like they are getting their money's worth (more pages == better deal).

Few modern authors are willing to buck the trend and publish a 100 page book, but they do exist. Take a look at Christopher Alexander's Notes on the Synthesis of Form.

I think you're reading the wrong books, then. I wish the books I read were 100 times longer.

That depends entirely on the quality of the writing.

I used to feel the same way, then I started reading books. So it might also be that you picked out the wrong books, or that whether you mostly read books or stuff on the web, whatever you go with you’ll put more effort in and hence find higher quality material.

In any case, mind sharing your favorite sources?

I used to be the same and to a certain degree, information on the internet is better. There is simply more information and it updates regularly. A book will be out of date soon. And information on the internet is often free of charge.

The value that comes with a book is its structure and its limited size. You don't get all information, you'll get the important information. And it is structured in a way that helps you learning.