Yet the Germans themselves were even dissatisfied with the squad abilities of the MG42 and ended up replacing it with the StG44 in their ideal planned squad (not that anything ever really reached planned TOE by mid-1944), relegating the belt fed MG to a platoon support weapon much like the modern US infantry doctrine.
Chroming barrels was something all sides were doing in WW2, but even the non-chromed barrels of the MG42 could handle several hundred rounds before needing to be switched out and that was at a very high rate of fire, which shortened the time between changeouts more than the same number of rounds from a low rate of fire weapon. Supposedly the Bren gunners didn't bother changing barrels, because the weapon didn't heat up quickly enough to make it necessary due to having a 500 rpm ROF.
Having two automatic rifles instead of one belt fed weapon adds nothing? Having a weapon that could keep up with the advance and allow for mutually supporting fire teams doesn't change a thing? In terms of cost the machined MG34 was not cheap and had to be replaced with the MG42; even that was due to be replaced by the MG45 that was much simplified and lighter, but the war ended before it could be produced. Having a light stamped steel automatic rifle would be a lot less expensive. The ZB26 for instance was cheaper to make than the MG34 and IIRC even the MG42.
Which goes back to the observation on Germany and the lessons of ww1. They went through the 30s not sold on the relatively lightweight magazine fed LMG and were content with a belt fed ( even if in saddleback) GPMP. There is a Masters thesis on line regarding US tribulations with LMG, they being the other army not sold on the concept.
If you are looking at the modern US fireteam, well its automatic rifle is a belt fed weapon in the army and the USMC intends to equip all riflemen with the M27. And the USMC is not proposing to fight WW2.
But the answer is depends. It also detracts.
If you are looking at mid - late war Western practice you also have to look at the addition of vehicle mounted MG always being available, as are ( for the british) large volumes of sustained from water cooled MG and the ability to introduce an additional companies worth of firepower from the carrier platoon, which can move fast across the battlefield. As well as actual practice which tended to have more LMG than the TOE would describe. Standard British practice was a squad of 8 with the additions be either dead, wounded, on courses or deliberately Left Out of Battle at platoon HQ or higher as deliberate policy.
And the infantry assault is the final 90 seconds of the attack which also features artillery bombardment intended to remove any sort of MG from the issue.
So yes having a large number of automatic weapons available is an advantage which is why the British and French with experience of operating on the offensive in WW1 moved in that direction quickly post war. But defensively the mobility issue is not so important the ability to sustain the fire is ( and that's including the protection for the gun and crew not just sustained fire) as is the ability to put a lot of fire out in a short period to engage a fleeting target in the final stage of the assault or at a range beyond which their grenadiers can engage. That includes the French fetish for rifle grenades.
German experience in the east is different. The Russians never had the density of firepower available to the Germans in the west so attacking them required far less concentration of firepower to overcome the defence. The main German lesson from WW1 was don't get stuck into a materiel war with Western powers in the first place. They were not studying how they tactically lost in 1918 but how they failed in 1914.
The solution being a panzergruppe.
By 1943/4 and the German issue is not so much having tactically mobile firepower but having survivable firepower and enough of it to stop a Russian infantry attack before they can close. The MG34 problem is that as soon as its identified it becomes the target for everything. Having more targets means you have more engaging before someone fires a 75mm tank round at you. The point of the tank being deal with the unsuppressed MG.
This is really a pre WW1 issue deriving from Balle D and the introduction of Machine guns in the first place. The original calculus was that with those a defensive position could stop an infantry assault far enough away that a bolt action rifle could not supress the position on its own without exposing the whole unit to fire, nor could the type of mg available move fast enough to keep up with advancing infantry. All the armies were looking at increasing infantry firepower to avoid that pre war and all looking at 'automatic rifles' which at the time could be either an LMG or semi auto weapon. The Chauchat as designed is a semi auto rifle not an MG. But pre war priority went to more important systems for their doctrine and national sensibilities. The German conception was for a tactical defensive battle after a successful strategic offensive so the LMG is less important than artillery. The British and French also had to consider small unit colonial actions where without large artillery formations they would still have to deal with rifle armed defenders able supress the infantry attack.
As it happened both the British and French were able to develop a sort of LMG in WW1 because they needed it and had access to the designs that existed and had thought about it a lot more than the Germans pre war. The Germans had neither access to the designs nor the need.
The production cost problem well depends on the considerations taken into account. If you are looking at a weapon with a design life of 15-20 years then a better made weapon even if it costs more initially is fine. If you are looking at a weapon with a battlefield life of 15-20 weeks then different calculation.