The fact that it can fire 3 missiles before the Grounder can get a lock becomes it's advantage. It is able to finish off injured vehicles quickly, and get locks on vehicles that other lock-ons can not. For example, you could just keep popping your head out of a window and popping off rockets, or get that really fast moving ESF that is on smoking health. It will end up being much easier to hit vehicles with SOME of the rockets. You might not be able to hit them with all, but you will at least be able to do damage where a Grounder wouldn't have time to lock on.