And I submit that FOX was planning on putting some premium mid-summer games (Yanks/Sox obviously included) games on FS1 when they inked the deal. Eyes on FS1 are worth way more to FOX than eyes on FOX at this point. The tournament that created Saturday's soccer game wasn't even in existence when that deal was signed.
No, we're not getting Sunday afternoon games on FS1 at anytime soon, because FOX doesn't have a bargaining chip like "We'll double the amount of national games" with the NFL - it already has a national audience every time it's being played. All they could do is offer way more than someone who was keeping all the games on the main network. But we did see the NFL take a similar tack with Thursday Night Football. Those games always had less eyes on them than they would have had they offered that package to one of the networks, but in the short term, it was worth it to them to use them to get the NFL Network into more homes and raise their carriage rates. And now that it's established, they are trying to double-dip by doing the simulcast deal.