I think maybe 5th worst might be a bit harsh. Look at teams like the Cardinals, they have one playoff appearance the entire time in the desert but still draw a respectable crowd. They sold out the last 2 seasons, even though attendance dropped at the end of last year, which I understand. I don't know many places where people would still be this passionate about a team that has consistently let them down. I know people that are fans of all sports, but no one is more passionate then Cardinal fans.
It is however, odd that the Diamond Backs are so unpopular here. How much more do they have to do to draw a fan base? Also, I think calling the Suns the "crown jewel" of Arizona Sports is dead wrong. The Phoenix Suns are where almost our entire "bandwagon" exists. The Suns sell well when they are winning, but when they aren't, you can't find a Suns "fan" anywhere in this entire state. People complain about the Cardinals, they bitch and wine, but they stay with the Cardinals. That's more then I can say for the Suns. I have never seen the kind of passion that I see in Cardinals fans, it's pretty amazing really. The D-Backs have to be our "Crown Jewel," just no one really cares about them for whatever reason.