That's now how game mechanics work I'm afraid. A squad can have 20 men but that won't make them better or more resilient than a 4 man squad necesserily. It comes down to health per mand and damage output. Those five Volks will almost equal the 2x8 man squads that cost 400mp.
Also, it sounds like you have v1 of the mod where they did a lot of damage to PE vehicles. you need to patch it to 1.04
Pumas cannot get damaged by rifles really well not in a noticable way really....unless they're on 5%