If all of the carriers d this then you are correct. If they differ in that regard there is certainly reason for non-hub-captives (and captives to a lesser extent) to switch any loyalty they already have.

One only has to look at the US cellular telephone industry to see an example of the industry disruptor at work. T-Mobile has really shaken things up for the big three. That disruption has gained it 4+ million new customers of late. One can certainly argue that they're doing so in order to pump up their valuation in the hopes of being bought, but I think the US government would have a hard time allowing such a sale go through. It's a shame that such an example wasn't around when the AA/US merger was approved.

It is interesting to note that at the new earning rates a lot of people are going to find themselves earning more points from credit card spend than from flying. That's an entirely different angle to look at things from, and it certainly affects loyalty.