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Well, since x2 LMG rifles are mostly like Obersts in terms of AI, they simply could focus your AI squads aswell, and due to fact that both falls\obersts\jaegers (except for fusiliers) have 4 men squads, he will put down you much quicker and you usually wont do enough damage to them to let volks\pios\anyone else to finish them off, after you retreated your AI units.
And MG always can be smoked\focused and later on be killed by Prist\Caliope.
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You are imagening situation where OKW already have at least 2 HQs builded + some sort of armor, which is hardly possible until like ~12-13 mins of the game. I only cant get one thing, why in your excample USF player dont have anything but rifles?
I'm not saying that rifles can take off tanks, but inf - for sure. And you cant really compare MG34 to Rifle LMG, simply because first one is basically core unit placed in 2 commanders, which is design fail. Even rifles with bars (and without bars aswell) can deliver a huge punch to OKW, if there are no obers runing around.
While MG34 is usually "must have", LMGs just a thing, which makes your rifles even better against OKW.
Also if USF player isn't complete idiot, he will go for Captain + AT gun. It will allow you to deny both Flak AND P2 without any single problem.
Sure in 4v4 it maybe much more easy to handle LMG blobs, because of the map size and fact that there are always teammate around and your front line is MUCH smaller then in 2v2. Go to 2v2 and try to counter LMG blobs here, its such pain in the ass that its not even funny. Also about flanking caliope\prist, its totally depends on map, flanking\rushing is not always possible, so you cant say "hurr flank it, problem solved".
And before you say "Well you could use Stuka and wipe things", ask yourself "Am I such a scrub to blob all my LMG rifles in one place", your stats are pretty good, so I think the answer will be "No". And here the problem. Good players, with LMG blobs, wont die to Stuka, they will avoid it most of the time simply by spreading around their rifles, but its still blob. Amount of afford from one player is significantly lower then from other, this is the main reason why everyone hates blobs.
We could go deeper in "theory crafting", but there is NOTHING OKW can do to LMG blobs, without proper answer from USF players. Its not like Ost vs USF where delayed PaK could mean pretty much GG for Ost.
Main question is why USF inf should be on pair with Obersoldaten in terms on DPS with x2 LMG. Is it so necessary?
Also I want to point it again -
I'm not talking about countering idiots and their blobs, I'm talking about ppl who know how to play.