Add a flamethrower to the Engineer for extreme close range vehicle damage. We have the Talon for exclusively anti air, the RPG for both ground and air targets, so now we need a third rocket launcher slot unlock exclusively for ground vehicles. A flamethrower would fit this bill, being short range but dealing extremely high DPS to any vehicle that unwisely approaches. I mean, what else is Engineer gonna use all the fuel in his back canister for?