I can't say that using LRM 5's is completely counterproductive. I did use a Catapult A1 that had 2 LRM 15's and 4 LRM 5's because I could spam the LRM 5's and reaaaally run the enemy dry on AMS Ammo before pelting them with my full spread. I mean, when your carrying 1800 LRM rounds. 1000 AMS rounds just isn't enough ;) Plus I just love continuously rocking the enemy. :P
I've trained the A1 and the C4, and have my final Catapult, the C1 (Because I can have a pair of back of ML and Tag). My personal feeling about using LRM's is that having more Tubes isn't always better. The extra heat, the tonnage costs. I'd rather have more ammo and programs to help me hit more. My C1 Carries 2 LRM 15's w/ Artemis, TAG and Beagle Active Probe along with the Target Decay and Sensor Range 2 mods. With 1800 rounds and that kind of accuracy added in, the only thing you need is some patience. No, I'm not sporting 50 tubes like I did with the A1, but I've got back up weapons, TAG and just as much ammo without running into the heat issues because I'm not firing the ML's all the time.
Anywho. When you know your facing the rain, you can't count on AMS to save you 100%, but it sure helps.