I have no idea if SWA will be competitive with anyone in the Hawaii market, we don't fly there.
What I do know is folks will flock to a cheaper product, that has been proven time and time again.
Hawaiians are consumers just like everyone else. Brand loyalty did nothing to save Aloha airlines according to CEO David Banmiller. "Aloha Airlines was founded in 1946 to give Hawaii's people a choice in inter-island air transportation," he said. "Unfortunately, unfair competition has succeeded in driving us out of business, bringing to an end a 61-year-old company with a proud legacy of serving millions of travelers in the true spirit of Aloha."
I doubt many will claim GO! had a superior product, but in the end they developed enough of a following to put Aloha out of business.
Aloha put Aloha out of business, the fare war that Go started was simply the straw that broke their back. It's way more complicated than what you think. Again, EVERY airline that has tried to establish themselves in Hawaii with low fares has failed. Every one and there has been a lot. Go never even attained a 10% market share. They are a classic example that low fares are NOT a prescription for success. In fact, any airline that thinks they will succeed in Hawaii by being "cheap" will almost certainly fail in Hawaii if history is any indication.