It's not like they're unfamiliar with those programs in the MAC & who does Marshall really care about playing in C-USA anyway? At least they have a real rival in Ohio. I get Florida and Texas recruiting but it seems like Marshall fielded better teams back when they were in the MAC as well. Their immediate success after leaving 1-AA reminds me of App State's recent ascension. They won the MAC 5 out of 7 years and finished ranked 3 times.
The MAC’s tv deal expires in 26-27. It was negotiated before the 2014 season. I think the MAC of 2013 is a world away from the MAC of 2020. I don’t see a single positive for Marshall making that move.
By "a world away", do you mean the MAC is now stronger, or weaker than in 2013? FWIW, their Sagarin rating in 2013 was 57.2 and last year was 58.3. Not really much different. For comparison, CUSA was 58.8 in 2013 and 57.6 last year. Again, not much different, either over time or conference to conference.
So conference strength shouldn't be a factor in anybody's decision (though travel could be). No move either conference might make now is going to have any significant impact on its relative strength.
When Marshall left the MAC for CUSA in 2005, CUSA was rated at 65.0 compared to the MAC's 63.2. But their new conference mates were generally more highly regarded, as evidenced by the fact that the AAC has called up seven of them, in what those schools clearly felt was a promotion.
I just question whether the MAC would want Marshall back.