I think that's a normal evolution of these games? In the end they are cooperative so your teammates depend on you. Although you'll find plenty of people at the top of the ladder spamming werid strategies and being successful.
Normal evolution yet somehow wasn't really a visible force on video games until streaming and is now the predominant force on pretty much every single online competitive game.
(Unless you play with cloistered private communities)
I think you're confounding streaming with the rise of solo-queue but cooperative (CS:GO, LoL...) games around 2010. Both were enabled by cheaper computing and alllowed competitive ladders to scale to millions of players. Games where you have to queue with a pre-made team (or pro teams for that matter) are considerably less toxic. Toxic streamers are more of a consequence of an already toxic community.
No, you are confounding what I'm talking about (fast discovery and dissemination of meta-optimal strategies) with toxicity. You could have 0 toxicity at all and still have a game totally ruined by the behavior I'm pointing out.
(Unless you play with cloistered private communities)