That hurts the SEC and only the SEC, and does nothing but help the other conferences. If each of these 3 conferences moved to a 9 game conference schedule and each conference agreed that 2 of the nonconference games would be against teams in the other 2 conferences with 1 cupcake against a Group of 5 conference, that would result in more money for all of those conferences and the SEC would be stuck with zero marquee matchups outside of it's own conference. If you can't see how that hurts the SEC and helps everyone else, then you know nothing about sports.
To make it even more of a hit to the SEC and a benefit to these 3 conferences, these PAC/BIG/ACC challenge games should all be scheduled for the 2nd and 3rd weekends of the season. All eyes of college football fans would be on these 3 conferences for 2 weeks in a row and nobody would be paying attention to the SEC and their rinky dinky little league. I'd be willing to bet that any of ESPN, FoxSports, or the streaming options would be willing to pay top dollar for the exclusive rights to those two weekends and would almost certainly be willing to pay exit fees for existing nonconference games in order to make this type of scheduling a reality immediately.