In 1v1 the impact of mass LMGs as soon as you can click redistribute is much higher than in team games.
In 1v1 the ability to suppress most of one person's army is high. Suppressing most of one person's army in a 2v2/3v3/4v4 is less drastic overall.
In 1v1 the ISU is not viable on many maps, CAS has no way to ever counter an ISU.
In 1v1 PaK walling against one person's tanks on smaller maps (your PaKs can cover a larger percentage of said map) is easier. There are also less people to sweep your tellers/S-Mines.
Soviet play containing between 2-4 snipers is less viable 1v1. Snipers are strong against CAS.
The short version is that the abilities from CAS are able to impact a greater portion of the map/your opponent's army in 1v1 and the hard-counters to CAS are stronger in 2v2 than in 1v1.
no comment on 1v1 as i do not play it but i play the rest of the game modes.
mass LMGs on 2-4 of a teams players is still really strong. it doesn't have as long a window of effectiveness as fuel income is higher but it doesn't necessarily need it if the axis player can grab most of the resources.
the pinning strafe from multiple players can lock down one area of the map for longer (not usually needed) or pin in different places. given how common it is for players to blob together in team games one strafe can sometimes hit 2 or 3 people's infantry. i really don't see it being in team games. the only "counter" i've seen to the pin strafe is for the enemy not to have enough units in the area to take advantage of the strafe, something that mostly comes down to poor play on the part of the CAS player.
issues with the ISU are lessened in team games as the other players can compensate (either by building ISU counters or by using multiple AT strafes).
you're right about pak walls, although some maps are designed with lots of choke points which end up making it easier. map design issue though.
not really sure how snipers fare against CAS as i haven't used them much recently. like paks they're pretty map dependent though.
i don't think there are "counters" to CAS, just areas it's not strong against, which is a big part of the problem with the doctrine. if AA actually prevent the planes from firing you could at least have a clearcut option to counter the doctrine but AA is useless against it and good micro and attention will only get you so far when maps are tight, pathing is bad, and you only have a couple of seconds to get out of a massive radius.
just to be clear, my point is that CAS is still very strong in teamgames. i'm not going to make judgements on a game mode i neither like nor play and i understand why you would find it more powerful in 1v1 but it is still a low micro, high impact doctrine regardless of game mode.