And its not true like at all. MG34\42 are defensive MGs, maxim is semi-offensive MG with Sustained Fire allowing it to actually defend something. But you realistically should always use sustained fire fire if possible, and you should do everything what is possible to have nessesery information to have maximum from it.
Maxim have advantages in terms of 6 models, the fact that cons can merge, good AOE, faster relocation, supperior damage and the fact that it wins 1v1 MG duels.
If you want to judge maxim by playing with it like its MG42 (place and forget) then for sure it will suck ass, if you will use it as it supposed to be used on its own way its a good MG with its own advanatages and disadvantages. If enemy is usuing MG42 offensively, it might be stronger, but you cant expect MG42 constantly rotating and moving during the fight, unlike maxim.
Use its mobility, other units (like mortars flares to see when to pop up sustain fire) and you will see that its not half as bad as forum warriors tend to present it.
But if you want to rant that MG42\36 is better then sure. MG42 is better and it easier to use, since most of the time its just possition and forget unless flanked\attacked by inderect. Does it mean that maxim is just unusable shit? No, not even near, you just have to use it differently.
Despite it being 6 men its wiped easier then other mg's. This is because:
It cant supress on time more often and gets naded frontaly far more often unless you feed it muni.
Its arc is smaller so it is flanked easier and needs to reposition more often leaving it vunerable.
The deathloop also makes sure that it gets wiped where other mg's get away. Its more like a 4 to 5 men mg tops. Merge helps ofsett this though.
Its mobility is only marganaly better and not enough to offset the points above.
Its damage is overated, i dont see it mowing down models as some claim it can. The only scenario it will drop models is if they try to nade it frontaly and the su player doesnt start retreating or another squad is also shooting the nading squad.
You are right that the maxim is usable just not in the same way as the mg42/34. But its not usable or better yet viable in other ways.
As you said use it in conjuction with other units works. This is good on paper. The flare you mentioned costs 40 muni and then onther 25ish muni for sustained fire, so thats 500 mp and 65 muni to have it work its its best without tech costs included.
The mg42 just requires it and a pio for 460mp to be at their peak wich is also a lot better and that for lower cost and lower micro.
Its just not economicly viable, you get to few in return for higher cost and higher micro.
If it was actualy more mobile or its damage was noticably higher it would be in a lot better place.