I feel for the OP on his dilemma. I cannot imagine the real frustration and disappointment.
Yes, the dealership black rubberized/asphalt undercoating can potentially cause real issues with rust.
Heck, look at a virtually new GMC/Chevy truck and you'll see rust everywhere underneath as their coating is horrid to say the least.
When I bought my Ram new in 19' I opted for the factory rubberized/asphalt undercoating because I really appreciate that everything stays nice and black under there and it also adds a much nicer overall look.
The caveat to this though is that I have, call it, a Brother who's been a Krown Rust Control spray tech for 30+ years, and he's see it all in spades.
He told me straight up that if I opt for the factory spray that I must spray the entire underside, in every crease, nook and cranny every year to ensure that factory coating stays supple and greasy, if you will. Then every second year after the first complete spray go back in late summer to early fall and just have the entire underbody soaked again. This is the only way to ensure that dealer applied product doesn't dry out/flake off, and/or keep moisture trapped in/under it and rot things from the inside out.
He even goes so far as to remove and toss out any factory frame plugs on any vehicle (asks the client first, of course) so as to ensure that he applies the Krown product inside the frame/sub-frame rails to ensure everything is thoroughly coated. Leaving in the rubber frame plugs only keeps moisture inside critical areas and doesn't allow it to breathe and drain.
There isn't a spot of rust anywhere on or in my truck and mine is a daily and sees a lot of mileage every year. I've been a huge proponent of preventative and predictive maintenance all my life, and I've always annually sprayed with Krown, too.
With the crap that is dumped onto our roads nowadays in the winter that's sprayed on the salt and/or that liquid brine crap, too. It's no wonder that ours and many vehicle succumbs to these harsh conditions.
FWIW - annual rust control spray (with a secondary underbody spray every other year) is the cheapest insurance in town to ensure your ride stays rust free.
Heck, I even Krown spray the fuses and all connectors, ECM, alternator, etc., under my hood, too. No rust and no corrosion anywhere.