Florida and F$U do not "cover" the South Florida markets, certainly not at the level that Miami does.
And that is the point. If you have Miami and Florida in the SEC as a PAIR of teams, then you will definitely lock down the South Florida markets.
It's the same point I was making about UCF and USF to the ACC. Right now, Florida is very strong in the Orlando and Tampa markets. But if you had a conference that was regularly featuring Miami, F$U, UCF, and USF, it would chip away at what Florida can deliver in the Central Florida Markets.
So if you minimized the SEC presence in Orlando, Tampa, West Palm, Fort Lauderdale, and Miami...what would Florida bring to the SEC? The Jacksonville market?
Again, I'm not saying that a 4-Florida-team ACC would be on the horizon. But it would completely lock down the 3rd largest state (by population) and minimize the SEC presence.
Obviously, the SEC improves its position in Florida by adding Miami. And it strengthens it more with F$U, I've never denied that. The only question is whether the SEC feels it is better to add F$U to improve its hold in Florida, or move into new states like NC and VA. That is all.
Just think about the map. A Florida-Miami combo is a north-south combo that appeals to both the more rural/northern part of the state as well as the more urban/southern part of the state. A Florida-F$U game, while it is a fine rivalry, just duplicates the coverage of one part of the state, without addressing the more populous portion of the state.