The thing about Dayton and markets and being "so close to Xavier" is misleading.
Market sizes are determined by census data that has nothing to do with television (or sports). It's a formula of statistics the census bureau came up with. And a while back, enough people commuted that Middletown, Ohio (halfway between Dayton and Cincinnati) was lumped into the Cincinnati DMA. The idea that Middletown TV viewers belongs to Cincinnati (and Xavier) and not Dayton (and UD) is absurd.
In Cincy-Dayton-Middletown you have fiver primary fan bases: Cincinnati, Xavier, Dayton, Kentucky, and then Ohio State/Other.
In June, the US Census Bureau is going to announce revised DMAs, and it's highly likely the Dayton and Cincinnati-Middletown DMAs are merged.
Does Xavier deliver that entire market by themselves? No. Adding both X and UD gives you the plurality of fans in Southwest Ohio. That's the #16 market in the country with 3,200,000 people.
You can find a 12th MARKET with more viewers than Dayton, but you can't find a 12th team that DELIVERS a bigger market than a Xavier-Dayton combo would.
The Cincy-Dayton DMA is the number SIX market for college basketball by total viewers. Ahead of Philly, KC, Charlotte, Atlanta, Dallas, Boston, etc. More people watch college hoops in Dayton than in Phoenix.
If Dayton isn't the C7's fourth choice, they're idiots.
I don't think you'd find anyone arguing that Dayton and Xavier aren't more or less the same market. It's the same with the LA DMA...Riverside used to be it's own DMA but was absorbed into LA.
But I think people are talking more of redundancy in that if you are a new conference looking to add quality programs AND new markets to increase the TV value, then it could come down to a choice. And that choice, despite Dayton's excellent support and appela, would be to put Xavier as the top pick. Now if it came down to opting between say Creighton (smaller market very much to the west), Duquesne (a less program in a good C7 city) and Dayton, then Dayton could very well be the pick based on the points you made.
But if it were between say St. Louis, a program with good facilities, growing support (and has shown not that long ago it can have great support) AND a larger and new TV market for the C7, then St. Louis likely would be the pick.
I think the C7 should keep it simple: Add what works, add what you know, add what has been proven. Go with Xavier, Butler and St. Louis for 10. Go with Dayton and EITHER Creighton or VCU for 12.