First part is demonstrably false. There's six major cities along the Atlantic coast - Boston, NYC, Philly, Baltimore, DC and Miami. If you want to add Jacksonville, be my guest. Inland in coastal states you've got Tampa Bay, Orlando, Atlanta, Charlotte, Pittsburgh and Buffalo. Outside of Atlanta those aren't big markets. Along the pacific you've got San Diego, L.A., San Francisco, Oakland, Portland and Seattle. Feel free to toss in San Jose. Inland there's Sacramento. That's 12 cities on the coasts with two fringe entrants, many of them don't have teams in multiple leagues. Can't run a pro league without a hefty dose of the midwest (and the Rockies and the Sun Belt). I'm a Reds fan because before competitive balance rules, the Reds built themselves a dynasty. The culture of obsolescence that's sprung up since then, IMO, is unfortunate and I suspect fans would enjoy going after titles without a booster seat.
As for soccer being dominated by big clubs at its very upper levels - yep, and it's the most popular sport on the planet. MLS has a fatal design flaw. It is nowhere near the top league on the planet. If you're outside an MLS market (or even in one), you can watch top Euro leagues. A no stakes domestic league is never going to be a big deal. The only way people are ever going to care about our top flight is if they're fully committed to their local team and know it's all connected.
And those dominant foreign clubs breed dominant national teams. Not an accident France, Germany, Spain and Italy have won the last four World Cups. You could substitute PSG, Bayern, Barcelona and Milan for the nations. If we want the USMNT to become a true powerhouse, we're going to need some lead dog clubs like Atlanta to drive that growth. Counting on a modest, balanced-for-billionaires league to do the job is foolish.