I fly UAL and AA quite a lot. UAL is always a 737 and AA is always a 321. The 737 is cramped, limited entertainment. The 321 is also cramped, no inflight entertainment. Both flights are always full and discussions will fellow passengers always yield similar results. The benefits eco system and the networks bring them back. We aren’t talking apples to apples anymore when comparing airlines. If you have the choose between the big three then perhaps you analyze that ecosystem component. If you are flying an LCC you purchase the cheapest flight that provides you the easiest path to your destination. JetBlues ability to command brand loyalty is limited based on the above assumptions and I think that is why JG constantly notes minimal price increases affect revenue.
In short, if you can’t dominate a market you have little control of brand loyalty or repeat business. The assumption of anything else is a jetblue fairy tale.