Titans probably do have the weakest abilities for the crucible over all. That being said you can still do well in the crucible as the abilities don't make a huge difference. It's really the gear that matters, but the titan abilities do have a few niches in the crucible that the other classes can't touch (striker destroys supers, defender bubble is a monster if you can keep enemy supers away from it, and the suppressor grenade has the ability to take away someone's super of you land it on a radiance warlock or arc blade hunter. Not to mention shoulder charge and lightning grenades)