Titans are very weak in crucible because they rely too much on close combat which is extremely easy to counter. Fist of panic is the only good thing a Titan has in PVP as it makes them nearly unkillable. Even a fusion grenade stuck to them wont kill them if they fist of panic at the time it sticks. Shoulder Charge is very easy to counter with a Shotgun as is the Titan Melee. As for the Bubble that is just pointless.