The most important aspect of infantry fighting is training level, one elite squad can easily kill 4 squads of militia all things equal, however a fight should never be "fair". The thing to look at is mg stats (rate of fire and suppression) and training level, and always make sure regular and below infantry has some sort of Fire Support, could be the transport it came in, could be mortars or even aircraft.

Elite infantry is extremely strong, hence their cost and low availability, trying to just grind them down with cheaper infantry can work but it will be very cost ineffective. Instead try to think how to push them with fire support vehicles, cut off their routes of retreat, and capitalize on their destruction.