Yeah they're of limited utility in urban combat but they've been very effective at killing lots of combatants and have neutered ISIS's ability to move large groups of combatants rapidly, which is how they took so much territory initially. They didn't have
that many experienced combatants or
that much gear so they shuttled both around rapidly to take large swathes of territory and make themselves look much more formidable than that. Now any such convoy or grouping is impossible except in densely populated areas (which Tikrit isn't by the way - everybody peaced out to avoid ISIS or avoid the Shias that are going to kick them out).
But we can't support the effort against Tikrit since half the folks fighting on "our" side there would slit every American's throat and happily enjoy some halva right after.
But raining death on assholes from above fundamentally changed the nature of this fight. Ever since then it's been 100% clear that ISIS will lose and lose badly, now it's just a matter of doing the dirty work. I still hope ISIS manages to get some crappy commandeered F-16 or something in the air though. That would be hilarious and I know a lot of American bros who would love to show them what a mistake that was.