My hot "youtube game designer" take is that they're actually good because understanding as many perspectives on game design as possible is a large part of the job of a game designer. They also help spread parlance around the industry in ways that are normally quite slow to propagate outside of vaulted GDC talks. And they give insight into games I simply would not play. Are those insights how I might think about all those problems, no probably not. And sure they might be VERY surface and player focused looks at the design space. But that's often really good! I want to know how people perceive these things!
Like, don't take every piece of insight and advice at face value. Don't apply it to every game without care. But if you don't already have strong opinions and insights of your own from games you love and hate, and don't already disagree with some things you hear in those kinds of videos, I don't think you're going to be a great game designer no matter what game design related info you're taking in.