Here's the thing, anyone who has played HS for more than 3-6 months is a "pretty good player" because you basically know all cards at that point and can play most classes competently. Just being "good" at HS doesn't mean much because this is a game with a low skill cap, in which just drawing cards in the right order can allow anyone to beat anyone.

This is not like a MOBA/RTS/FPS/Fighting game where you actually have to be in the top 1% of the world to be a "pro" at the game.. this is a game where the community has decided popularity is > skill/knowledge. So, we have a strange mix of people in the "HS pro scene", some of whom are super dedicated to the game and play every qualifier and use spreadsheets and stuff to min/max everything.

Then you have people who are dedicated to streaming and getting popular, and don't take the game as seriously, but because they're invited to everything, and because just playing HS adequately is enough to beat anyone if you're lucky, they still win things occasionally. Forsen is just a streamer who has a lot of opportunities because he's popular. Not impressed in the slightest that he occasionally wins something, because he's invited to literally everything.