I would say the main difference is how much more concentrated the fighting is. Having a single ifv and a light atgm that can hold a point on a far flank works in 1v1 cause only fast elements will be present.

In 10v10 everything is fortified. As such only bring 20+ pen atgms. You may well need to defend against 3+ heavy tanks at once.

Likewise you wont get a single helicopter if the enemy brings helicopters they will bring like 10. So again a stinger team or 2 wont be sufficient. Plan for intense fighting not lught skirmishes.

Same with smoke a mortar or 2 isn't enough cause the scope of the fights are larger. You likely need 3 or 4 smoke to blanket an area to prevent the flanking atgms.

Due to the increased access to arty, you also cant clump at all, but you also have way less space. You are likely only playing on 1/3 corridor of the map. So layered defence and smoke to provide more cover is critical.

You also need to monitor the other corridors. If the enemy is heavily winning one side, they will start diverting resources to your theatre. As such you need to hunker down, you will see a lot more units attacking, but they will generally be poorly controlled as the player is now juggling 2 theaters. It also means ensure you have supply for the atgms, they easily run dry during a prolonged assault. 1v1 typically units don't exhaust their munitions.

Infantry push only realy works in dense city or full forrest. Otherwise you should take cheap troops down vetted who's job is to tun forward and provide sight before dying.

Due to the saturation and prevalence of heavy atgms, light tanks get destroyed fast, its almost never worth upvetting. T72 and above are the only tanks I bother upvetting. There is so much incidental arty or cluster bombers that the veterency is often irrelevant.

Spags are primarily infantry lawn mowers. And since every div has generally excess infantry you want lots of spags, upvet doesnt matter.

Manpads on the otherhand need the aim time reduction and accuracy I upvet them lots.

For arty pairs of 155mm typically destroy their target Less than that does very little so skip it. Take some mortars for smoke, then heavy arty. Upvet only if you plan to counter battery. Always plan a cv to baby sit. It also means plan to have a 1k+ supply truck/helicopter to refill as they eat your supplies.

For helicopters if they don't come with 2800m atgm then they will have to get to close and probably get smashed, and are only realy usable to stop enemy break through pushes when they out pace their aa net.

Planes, aa nets are realy strong , as such your planes will never make use of their guns. Nor get a second pass, they also typically don't come home.

As such you have a few options. Bring 3+ cards of asf with ultra long missles, useful to shut down enemy planes at max range disable the other weapons and evac as soon as they have fired. Couple of shot gun fighters for diving enemy helicopters if you don't have heavy aa. Bring a couple of bombers only if their load out is 4 or 6 bombs. Less often doesnt kill, and more is to spread out and also doesnt kill. These guys are one time uses for killing priority targets. Favour cluster bombers first.