So if warlocks and hunters left your "almighty titans," do you think the tower would last? Warlocks are the ones who provide the intelligence, and hunters are more capable of sniping than either of the other classes. So, lose capability of removing high-value targets (or just lower chances of killing them at distance), and losing most intel that a titan bases "their decisions" on. Remember cayde, he didnt care about zavalas thoughts until after he already acted