Then why it shouldn't be able to finish off/kill infantry units?
It can if the opposing player doesn't understand the retreat function. It deals steady damage, not burst damage. It's not a squadwiper.
Even if you do not completely wipe the enemy squad,you will bleed it and over the time you will cause more damage to him than your UC is worth.
That's literally the whole point of anti-infantry vehicles.
The problem is not getting a raketen but how to deal with UC or Clown car during the time where your raketen is in building process and travels to the front.
Play tighter. It can 1v1 your infantry squads. It can't 3v1 your infantry squads.