I think the biggest decider for titans being the worst class is something that you haven't touched on that was mentioned... The titans have really terrible exotics. Armamentarium is practically the only advantageous piece to wear in crucible for striker. Helm of Innermost Light is good, but it really only provides a so-so extra perk. Saint 14 is the only choice for defender. If, when TTK comes, there are some genuinely good titan pieces ala Ram, Symbiote etc then you've got a class that can easily match up with the other three