Ignoring any flaws in legal theories, let's say a judge allows you to break them up. How are you going to do that? Splitting an airline in half isn't like forcing a company to sell off divisions (a la Facebook and insta, retail banks and investment banks). Does Delta A get half the flights and Delta B get half the flights? Does that mean that the two flights per day on one airline that I can choose now forces me to just buy that one flight per day if I want to stick to one airline? And are there enough planes and crew to even make that possible? Or would both airlines have to increase their costs because they have to buy more planes and hire more crew? How do companies usually deal with increased cost? Doesn't sound good for consumers to me.

Or does Delta A get half the routes and Delta B get the other half? So now whichever airline I choose I can't get to maybe 25% of the places I want to go.

And if you think IROP handling is bad now, good luck when the airline has half the crew and equipment that it used to have to move things around.