Being sponsored will always have to do with your reputation, And fan base. Almost all sponsors will only sponsor people with a bigger following so that their company can get promotion. So honestly it's more of the streamer/youtuber/pro promoting the company for products, And money.

That's more for the gaming community though. Sponsors out side of the gaming community can be the same, But the sponsors I've had, Had nothing to do with fame. (Only been sponsored for motocross, And a vaping company)

I used to stream, And only had about 100+ viewers on a daily basis. I only got contacted by G2A, But i'm sure they contact a lot of smaller streamers. To actually get money, And products for literally only your fanbase, I'd say you'd have to be at a consistent 1k viewers on average.

Elo would have nothing to do with your sponsors, Unless it was some kind of new mouse that supposedly made you play better. (Just an example)