YouTube is factually on the decline. One of my kids has a reasonably popular monetized channel and I follow the revenues as I am the actual channel owner. Gaming channels are down (revs) by nearly 25% YoY. His views are up and his revs are down 20%.
There are kids there making millions, some even per month, the whole thing is out of hand, a drop of such proportions wont kill a great thing.
You're thinking of one of the Paul bros? I was referring to PewDiePie. In any event, his metrics are public and he has nominally more views and less revenue.
Twitch is a huge problem for YT. My son has a Twitch feed. He has 400 solo Fortnite BR wins on console. Much better revenue on Twitch.