I'm on Stadia. There are dozens of us... dozens!
On that note, I don't disagree with what you're saying. More platforms means a broader audience, which means more potential people for multiplayer, and maybe there's potential for crossplay, which I always like to see in the industry. DOS2 eventually came to other platforms, even the Switch and Steamdeck, which are handheld consoles, so I don't see why BG3 can't eventually make its way to other platforms, including handhelds or stationary consoles.
You're getting flamed for your opinion on Stadia, but your point is not without merit. I think it's just that Stadia users don't want to be left behind by such rhetoric, having already bought in on the platform.