Personally, I think it depends on the attractiveness of the Vlogger, and that they kinda overlap, if that makes sense. Not very hard for attractive vloggers, though it might take a bit of time for them to get noticed at all. And the non-attractive vloggers have a much harder time because they're just genetically less enjoyable to watch.
I think its harder for gamers than the attractive ones, and easier than the non-attrative ones, though it depends on the type of games one play. Horror/CoD/Minecraft/happy wheels/indie is very hard, while for instance, Nintendo, or forgotten classics/masterpieces(I'm this kind), are a bit easier, simply because there's still a large audience, and its easier to be noticed, but not to spread much. So basically the ball starts slow and goes slightly faster all the time, until it gets to amazing speeds, because these games are timeless. Indies/horrors/FPS seem much to me like a YouTube phase, much like Gangnam Style blew up, and is almost forgotten.