It sometimes seems like this
But then, with what are you suppressing and for how long? I can assure you that when trying out my WW2 scenario on Petrzalka map, AI infantry got on many places stopped dead in its tracks by overlapping HMG killing zones and light artillery/mortars - noteworthy is that light arty is better at suppressing than the heavy one as it tends to distribute more rounds around target.
Also it tends to be random - firing whole turn at one infantry squad, killing half of it and it's just pinned... Then in next turn the same MG on the same spot managed to rout two squads and still had enough rounds to continue pinning that first one...