It appears impossible to balance the game for both 1v1 and ie. 4v4 simultaneously.
As myself and a couple of others have alluded to, it's really a question of design as to whether things work in both modes. Two immediate problems spring to mind - the first is some factions having more powerful late games than others, and the second is that some factions are designed around resource limitations. By "some factions" I mean "OKW". USF also has a "weak late game" on paper, although after patching it's now fairly strong (albeit still the worst of all four, as win statistics indicate) as long as you go for Airborne and have great micro with your Jacksons.
The reason these two concepts are problematic are because the more players you add, the longer a game will be able to go for on average. Any one player's mistakes are diluted by his teammates. A catestrophic breakdown in one sector with multiple squadwipes is almost guaranteed doom in 1v1. It's a big problem in a 2v2. In a 4v4, it's often not a big deal. Early game advantages enjoyed by USSR and USF (which sometimes cause them to be OP in 1v1), now don't count for much, since the early game goes for a couple of minutes, while the "late game" goes for however long the match does, after about the 15-20 minute mark.
Because teammates get shared resources from a sector, and because caches allow for the sharing of resources, and because there are fewer sectors per person in larger team games, this means that any resource limited faction is less resource limited the larger the game modes become. In a 2v2, OKW with an OH partner is still pretty constrained, although not as much as 1v1. In a 4v4, an OKW player may as well have full fuel income. Because there will be so many caches around that it basically doesn't matter. "Stronger, but fewer units" becomes "stronger, and basically as many units". Hence, in 4v4, OKW still dominates even in the current patch, as they languish and wither in 1v1 modes.
I would argue that Ostheer and Soviet don't really change much between game modes. You get "more stuff" and things are more disposable, but the actual discrepancy between them is smaller than it is between the WFA factions. And I would say that the reason this is boils down to their factions not being designed in ways that cause scaling problems. As such, I suggest that in future, factions should be designed with these principles in mind - balance by resource manipulation will cause problems, and balance by strength at game phases will be a problem, because in all cases, those two things will inevitably be diluted or become imbalanced by the act of scaling up the player count.
Vaulting went right, except for the fact that it can't be done on retreat, only as a direct player controlled action. Also the way squads turn into the human centipede when vaulting can be silly and usually an invitation for squads to get wiped.
TruSight went right, except for the fact that it's actually kind of glitchy with how it affects the AI. LOS blockers act as invisible shot blockers, which leaves things like tanks rotating their turret because a tank drove past a tree or the smoke from a wreck causing things like ATGs to decide their only choice is to rush forward to melee range. Not to mention most maps have LOS blockers in seemingly random/unintentional positions. The way a single tree can cut off the vision of an entire army advancing can be pretty silly. Having units walk 'into' an LOS blocker and disappearing/becoming blind is also kind of silly. For smoke, sure, but on corners of buildings and hedges it's silly.
Snow and mud worked well, except for the fact that infantry squads can't figure out how to avoid them while pathing, and they effective act as molasses for squads when one entity gets mired in it. The (arbitrary) placement of deep snow and mud on maps probably ruins these mechanics more than anything.
Ice works well, except that there's no deep v shallow distinction for ice, which leads to tanks being swallowed by the earth because their front end was on 2 inches of ice.
Blizzards, well, never worked well. They were a sort of cool feature, but for multiplayer gameplay it never played out to be, well, fun. I feel that if blizzards were ever to happen, maps should just start in a blizzard for the first minute or two, and then never occur again, or happen at like the one hour mark. They occur too often and for too long for any game that utilizes Victory Points, such as all of automatch.
Even despite the no vaulting on retreat, it's still a great change. So I will definitely give Relic kudos for it. True sight is absolutely glitchy as all heck, the real problem IMO is when tank wrecks instantly block line of sight. If they gradually reduced LOS as smoke stated pouring out that would be one thing, but so many times I've seen a tank die then suddenly two tanks that obviously do have a straight bead on each other start going full-stupid repositioninig around the wreck in the most inefficient way possible. It's SO BAD when it's a turretless TD like the SU or JPIV or something as well.
Blizzards are a mixed bag. I can't stand their current implementation, but it's really just the extra micro-tax caused by units freezing that is the problem. It makes players hesitant/cautious and slows the pace of the game dramatically until its over. However, the idea of weather conditions reducing line of sight dramatically does create an interesting tactical variance. It's just... it's paired with this other garbage all in one annoying bundle.