Well, I haven't heard the Proair/JetBlue comparison before. I guess there are some cursory similarities, but there are far more differences.
JetBlue was intended from the start to emulate and improve on SWA's proven business model and translate it to a huge, underserved O/D environment. ProAir tried to make a go of it largely as a corporate shuttle for GM, and oh, yeah, we'll carry regular pax to IND and PHL, too. DET/Detroit is nowhere near the size of JFK/New York, and already had Southwest and Spirit next door at DTW. New York had no low fare coverage at any of its airports.
Crucially, JetBlue departed from nearly every other startup airline with its realization that low fares might attract customers, but it won't keep them. You have to give them a reason to keep coming back. That means excellent customer service, on time flights, and excellent reliability. ProAir was just like the others, in that they hoped low fares alone would be enough. It's not and never will be if you want to last.
And last, JetBlue started with a huge pile of money, more than any other startup ever. It was enough to implement the business plan correctly from the get-go, rather than assume that as the airline grows, well, we can just fix it later. More than 30 million was spent before the first plane left the ground, most of it on infrastructure, planning, software, and hiring experienced people. It was a serious airline right out of the gate, the money made sure of that.
ProAir tried, but wasn't able to really get the airline going. It got up to a peak of maybe six planes and had to quit paying its bills. There was no reason to fly them (no income) and no way to build the airline to make it better (because of no income). ProAir was a classic startup failure, like many other before it.