They seem to fill the void between in-depth study and knowing absolutely nothing.
Thus 'getting smarter' could be an overstatement in this case.
When I get an urge to make something, I go into the garage, and freeze. How do I put two pieces of wood together again?
There clearly comes a point that even in depth studying of a topic has limited ability to translate to real world skill. Very few things can translate well from study go skill.
And so rather than watching digested videos, I recommend reading the works and essays of great minds, and struggling (reasonably), to embrace their way of thought, while appreciating the content. Understand some, then go again, and understand more. Socrates taught Plato, and Plato taught Aristotles. Is it a coincidence? I would find the greatest mind I can find, first among other strategies. Personally, I've started reading Emerson, everyday, or Montesquieu. I write parts I like, on paper, and try to understand better along, why he says what he says, and why he writes how he writes.
But this is supposing I'm smart, and have my word to say... Well, let us settle on the compromise then, and experiment? Because also, different people are at different levels of grasping, and also, they have different definitions for 'smart', so you should do depending on what you want to become, and which 'they' you want to be a part of.
Personally, I don't care that much, it just feels good to be so near a great mind, though surely everyone has his own view of what that is.
not joking. Frankly, it makes my degree more valuable
Many, certainly not all, but many of these videos are educational in the same sense. They give a layman a basic grasp of a complex subject. E.g. this video on the immune system won't make you a biologist, but it's still pretty informative: https://www.youtube.com/watch?v=zQGOcOUBi6s
These are the kinds of videos that teachers might show in a classroom. Certainly they are way better made than the cheesy, poorly made educational videos I saw in school.
And to be fair, all of this stuff is entertainment, even Cosmos. There's no practical value to me to learn about how stars are made, or how the immune system works. But I find these things interesting.
Most YouTube channels are trying to make you think you are getting smarter because flattering your viewership's egos is a proven way to grow it. They work from a top-down perspective where they hold the information and you listen without questioning; much like a classroom; for people who mostly think "learning" is such process.
It is an entirely different experience to watch a YouTube channel where the host is actually working hard to make you think, even when this forces the host to be stern with its listeners, to correct their incorrect patterns of thinking when they call in, and to be available for any corrections by their viewers and willing to publicly correct an error.
For all that, I like Stefan Molyneux's podcasts on YouTube.