If Alaska acquires Hawaiian then this would have to be decided ultimately by SCOTUS right? I would think these two cases are too similar and there needs to be some fairness and consistency in the rulings.
The more interesting transaction that arguably should've been stopped was Alaska purchasing Virgin America as they were both largely west coast airlines. But amazingly enough (as someone who held status on VA and later Alaska), my flights actually got cheaper after that merger, and I was consistently upgraded too. So if that merger hadn't happened, my experience would've been worse.
To put this in perspective, 60 out of 566 JetBlue and Spirit routes overlap. Alaska and Hawaiian share 12 routes out of 336.
An analogy would be two competing gas stations at a very busy intersection with no plots nearby to build more stations. Just by existing they either drive each other down on price or collude on it. One going under means a new station could exist, but one buying the other guarantees prices do not go down.
I assume you're talking about JetBlue's Mint product which is all business class for some cross country flights and a few international. Again, I think they are trying to provide the best value for business class compared to the larger carriers.