They don't HAVE to be effective versus infantry in Renegade, it's a simple matter of getting rid of that stupid rocket launcher clip idea (What kind of rocket launcher has fucking MAGAZINES??) and replacing it with a single shot rocket launcher that does more damage, but doesn't have a bunch of explosive damage in the area around where it detonates.
Of course, you could always give Gunner the "clip launcher" with six missiles, with them doing less damage per shot, but more in a consecutive volley of missiles.
Either way, my point is that rocket soldiers shouldn't be effective against infantry to begin with. If they hit in the body, sure... Like in C&C where hitting a soldier directly will nearly kill him.