NBC sports network channel isnt exclusive to YTTV, its just the first carrier to launch. Xfinity will be next, and they have already stated they will try to sign up multiple carriers, probably every one they can. Its tough to sell advertising when you cap your audience at ~10M households.
And the big ten conference splits their games between Fox, CBS, and NBC
Fox: Will air games in the "Big Noon" window and alternate years for the championship game. Fox also has majority ownership of the Big Ten Network.
CBS: Will air games in the afternoon slot, including a Black Friday game, and alternate years for the championship game.
NBC: Will air games in the primetime "Big Ten Saturday Night" slot and alternate years for the championship game.
Peacock: Will exclusively stream some games each season and simulcast some games that also appear on the NBC broadcast network.
Big Ten Network (BTN): Continues to air a comprehensive slate of games in addition to the broadcast and streaming options.
The "big ten sat night" is already on the main NBC network, so all you are likely gaining on the new sports network are the games on Peacock, which will now likely be simulcast on their new network.
I cant imagine this would pressure Disney at all. As they now offer a subscription bundle ($40) with Fox that gives you access to all ESPN networks, the SEC networks, Fox sports, FS1, FS2, and Big Ten network. Thats at least 20X more sports than this new NBC channel will have, when you consider its all of the ESPN+ games as well.