LOL and because of this no one buys a guided "stringer" rockets right? LOL..
"a helicopter like an Apache is never going to shoot down SAM missiles (with current systems)."
maybe my multiple argument is to complex because this part of the argument is not about "current systems"
it is possible to shot down a SAM with an helicopter but only for "Robotic-Helicopters" because of the reaction time the KI need to overrule the human"gunner" to shot down the SAM.
"The mounted cannon has a low ROF"
This is not a problem because the SAM do have the cannon as a target this means the vector of the rocket is straight to the gun. In this case you can shot down a SAM with a 9mm hand gun with a single bulled. M230 chain gun do have 625 rpm you really don't need more. (if the target vector is straight to the gun)
and the JakB-12,7 (Mi-24) do have 5000 rpm this means you can simple switch the "gun" to have a higher RPM rate.
but in fact this is not the problem the problem is : robotic flying with a human gunner you can never shot down a SAM.
in fact: modern (near future) helicopters do have a SAM hard kill system with the "mounted cannon".