I have used both the GPMG and the LMG.
The LMG with a good 2 man crew produces sufficient fire downrange, is lighter to carry, has no belt to entangle itself in foliage etc, and it was a joy to strip and clean after the GPMG. (The latter filled up with gunk and was not a fun thing to clean - definitely a 2 man task.)
Having a top-mounted box mag, the LMG was simple to keep fed with the No 1 simply whipping the mag off and calling "change" as he did so, no2 then plonking a new one directly onto the gun easily
. No fiddling underneath the weapon (like say a BAR would require, with the no2 there only able to pass the mag to no1 to then fiddle into place himself). The top-mounted mag and the change process meant no1 could remain laid onto the target as well. Unlike a BAR, it had a quick-change barrel with a handle so you did not need an asbestos mitt (a feature the GPMG carried on).
The LMG, when originally in 303 as the BREN was designed for the old WW1 type marching fire, carried at the hip on its sling. When doing so, the top mounted mag meant an easy change, unlike the BAR which would require fiddling under the weapon. The GPMG could be slung and used from the hip, but was a bit of a beast to do so. (NB we were particularly instructed back then to restrict the term BREN to ones in 303 (which were still around in caded forces etc.), LMG for the 7.62 conversion. Nobody back in the 1970s ever used the "L-numbers" - doing so meant you were a "train-spotter"
! - and if you did
do so then it would probably lead to a quick run round the drill hall with the weapon held above your head
The GPMG did have the ability to loose off great bursts of fire when required, but 99.99% of section tactics had no real need of fire hosing...
The LMG was quite accurate, and it was used as a sniping weapon in single-shot mode in WW2. That was also in the pamphlets for initial use in the defence, so as not to give away the position of the gun group too early in the contact. GPMG only had automatic, though with a little practice you could get it to "single tap" - frowned on if you did that on the range though!.
The LMG also had a slow rate of fire, which the data-ferrets would probably "penalize" it for. But in reality
the low ROF meant the weapon was extremely easy to control on auto, and you could direct the fire extremely easily as it went of in its distinctive "duf duf duf". Note that the USA came to the same conclusion with its SPIW automatic rifle concept of the 60s and 70s. A low ROF leads to controllable
auto-fire. And also does not burn through mags at silly rates.
The GPMGs ability to fire big busts really was of any use when tripod mounted, with a set of heavy barrels used to deal with the excess heat. In light mode you were to use bursts of 3-5 and maybe the odd 10 shot in special circumstances such as in an ambush situation. The LMG with 30 rounds in the can could do that just fine
. So no need for some artificial lowering of its HE value in game terms.
There is a lot more than just a simple reading of book numbers and guesstimates on magazine capacity etc in determining what an MG should score as a real-world system.
In real-world application then an LMG and a GPMG are really pretty much equivalent devices. The German LMGs with their 1200 round rate of fire do get a mention in many WW2 memoirs, but it seems the high rate of fire was more of a morale effect rather than any noticeable on-target effect, and it did chew through the ammo!. A BAR though would be a little less use as an LMG - but then it was an SAW in any case.
A SAW is operated by one man to produce occasional burps of fire with inevitable pauses as the gunner feeds the beastie. The SAW has problems with keeping up a sustained
base of fire (whether its the gunner having to fiddle with underneath-mounted mags, or single-handedly dealing with long belts all by himself).
Quite frankly - I would probably have just an "LMG" and a "SAW" weapon class with just 2 data points. No need to differentiate micro-details between a BREN, a Spandau, an M60 or an FN GPMG. All have the same game effect, as they also do in reality. It is also what 99% of tabletop wargame rules do.