@Thenomain A battle.net tool would also have one massive advantage; an in-game interface (in fact several games supporting it internally).
All those Overwatch, WoW, SC2 etc players are very often in one-time groups formed on the spot, who currently if they want to chat while they play to coordinate etc they need to figure out which voicechat to use (which... not everyone is using the same one), then alt-tab out to go log on there and find each other. It's not a lot of work but it's some work which as you said might not be the easiest thing to do for casual computer users.
If instead these games, played by millions, offer everyone an one-click-and-it-just-works way of chatting with your group then the new voicechat will immediately become the de facto way of doing it. I mean overnight. And once people are hooked to it they might start using it for other things outside of Blizzard's ecosystem (which is almost certainly their plan all along) even if dedicated tools offer better featuresets overall.
Blizzard had tried this before, kinda, a few years ago... but the voicechat feature they offered at the time was barely even functional. It was a horrible implementation which caused it to be dead on arrival.