I agree for one main reason: the mergers are removing competitors from the field, so eventually it won't be too hard for the three remaining players to shift their programs en masse, meaning that there isn't a competitive alternative.

In the years when there were 5 or 6 viable U.S. majors, we saw some of the programs go slightly different directions and compete for elites with different strengths and focus points. UA and AA tended to track each other closely, but DL, NW, US, and CO all had programs with some different variables to them. If you lived in a city served by several of them, you could pick a program that fit your needs/desires best.

Now, it's a three-horse race. Assume the AAdvantage brand and structure will supercede the Dividend Miles structure: you'll have UA and AA, which are still pretty similar, and DL. The strengths of their respective route maps are pretty entrenched...not a huge need for the three to poach each others' elites in much of the country. Thus if two shift away from the current program structure, I don't see a compelling case for the third one to go lone wolf and attempt to win the others' travelers. They'd probably move as well.