Don't know if it's legit, but makes perfect sense that ESPN would be on board with this in a couple ways actually.
First, ESPN is trying to consolidate their most valuable programs into one product. Even if the ACC deal is below market rate, if ESPN really just values 4-6 programs in that conference, it can shift those over to the SEC, bump their pay, and not pay the 6-8 programs it doesn't care about. And I wouldn't be surprised if the operating assumption is that these programs would draw even more eyeballs in the SEC than they do in the ACC.
I don't know if the numbers work on that. The value of the other 6-8 isn't zero, and ESPN will wind up as a bidder on wherever they go anyway.
Second, ESPN values the playoff more than anything. They want to expand the playoff, own the playoff, and shove as many SEC teams in there as they can fit. Having the SEC dominate the playoffs also (theoretically) boosts the viewership of SEC regular season games. The goal is to establish the SEC as the premier league in college football, and the driving force of the postseason. Strong teams in rival conferences are the antithesis of that goal.
Thing is, the ship has sailed on ESPN being the sole rights holder on an expanded playoff. Fox and the B1G will (wisely, for everyone's sake, even the SEC) not allow that to happen. The conference duopoly will be a playoff broadcast duopoly.
And I totally agree that the SEC's angle is total hegemony of national title level football, and so why would UNC and Virginia make any sense? It does not have the odor of truth.
Third, it's clear the only possible rival to the SEC's ambitions right now is the B1G. The number of valuable programs outside the B1G and SEC are dwindling, and the SEC is probably wary of B1G expansion to some extent. Figuring that it's a matter if time before the B1G starts looking at ACC schools, the SEC (and ESPN) may have thought it wise to act first and take the most valuable programs off the table.
The SEC's dream move would be adding ND and Clemson. Alas, we do not always get what we dream of.
The play ESPN has here is that they have full ownership of the SEC media rights (which no one has ever had before, they've always been split), full ownership of the ACC media rights, and are probably in a position to be the high bidder for whatever shakes out with the Big 12 and Pac 12. Plus their dominant position in broadcasting the lesser contracts. They have a truly national scope and (unlike any other media player) the platforms to deliver it all.
ESPN's move is what ESPN's move always is for sports entities that don't play ball with them: ice them out of the conversation entirely. ESPN is never going to give focused coverage to a Big Ten game again. They are going to cover a college sports nation that doesn't have the Big Ten in it. They are absolutely brazen and shameless about this, as we all know. It's a very different media landscape than it was 10-20 years ago, but over time that can have an effect.
(I kinda can't imagine the B1G selling their non-Fox package to ESPN at this point given the cold war happening, but who knows I guess)
Anyway, you are precisely correct that the action is now Fox/B1G vs ESPN/SEC. That is the only battle that matters, everything else is just deck chairs. I see the analysis flowing from that differently though.