You're wrong here, Twitch doesn't ban gambling streamer e.g. Drake because he's gambling on sport betting, not luck based games e.g. slots, roulette, dice etc. The problem is Twitch banning the site e.g. Stake, if Stake separate his casino site and sportsbook site, of course they will can advertise on Twitch.
What do you mean exactly with this? If Stake, as a separate entity, goes live on Twitch that is okay? Stake is a gambling entity, and it's not safe from Twitch's ban since they are a gambling platform.
What i only understand is Drake's content on Twitch wont get banned only if he use sports betting content on his streams. Since twitch wont ban streams related to fantasy sports, poker and including sports betting.
Also, Stake wont get banned as a platform on Twitch, only the game related content like dice, slot, roulette, etc.