So right now playing Brits is basically hard mode compared to USF.

With that said, you almost never see people go Aussies unless it's for the Archer and that is for a few reasons.

-Lack of snares: Since sappers don't have AT grenades like CoH 2, you have to get an infantry section and tech grenades if you want snares. Due to the costs and for efficiency, going for one AT section + snare tech is way too much of an investment when a mechanized Wehr player can kill it easily with two 8rads or DAK can nullify it with the AA halftrack. I would definitely make snares more accessible, like giving the Aussies a slightly weaker snare (like coastals) locked behind nade tech.

-Australian Infantry: This unit is okay as a combat squad, but don't do THAT much better than a standard infantry section and have less health per model so tend to drop a man sooner. They seem to be balanced around being a mid-long range combat squad that excels at fighting from cover to cover. What happens in reality is they get beaten by Wehr by a Grenadier + Pio and DAK by a Palmgren with the combat buff. Another option is to just avoid fighting them and cap the rest of the map since you'll usually be up a unit when fighting Aussies, forcing map pressure leading to favorable fights. While Brits can win the first engagement using their starting sapper, the whole rest of the map is being taken by the extra units the opponent will have.

-Poor mid game scaling: Because most people know Aussie players won't have snares, as soon as any anti infantry vehicle comes out, you have to play much more carefully because if your opponent is good they WILL dive your retreating squads and wipe them, knowing your only option is the 2 pounder or mines. Since Aussies are so slow to vet up, and with infantry training locked behind tech, usually you trade a slight early game power advantage (which usually puts you at an even spot due to Brits inherent territory control weakness) for a horrible mid-game, struggling to keep up with vetted enemy infantry or dealing with light vehicles. The scoped rifle upgrade for the Aussie infantry section is also extremely overpriced for what it does, and frankly needs some changes as I believe the close range damage of the squad goes down when purchasing it, that or moving accuracy.

-Emplacements are weak: So I am okay with this, as CoH 2 Brit emplacements could be awful to go against, but CoH 3 does have a lot more sight and smoke tools, and good indirect fire for the Axis so that they are much easier to deal with. The lack of a brace alongside the abundance of bombing runs and squads with satchels/shreks also make them pretty easy to take down. Considering the Brits have a very cheap MG emplacement that is rarely used, it is no-wonder you never see the Bofors or 17 pounder. While the heavy AT gun emplacement has some use, the Bofors is pitiful, it hardly does much damage to infantry squads and considering it is easily dealt with and easily avoided, it should really shred through squads to at least encourage it's use. 

All in all, the only real positives of the battlegroup aside from getting an Aussie to vet 3, is the late game power of vehicle over repair + the Archer. If you simply play a standard Brit build the vehicle over-repair can make Crusaders perform much better, and then the Archer can arrive to take care of anything too big for them. It is a shame that the ideal way to use the battlegroup is to ignore a lot of the abilities in it. 

The only viable builds I have made work in 1v1 or 2v2 with Aussies as the mainline infantry is to focus heavily on staying alive using the 2 pounder + mines until a stuart comes out, using the utility focused upgrade to buff up the infantry further, and then either more stuarts or a bishop until I can get the Archer as I get unit upgrades. A variation is to instead use one Stuart and playing more defensively until I can tech up and start pumping out crusaders with over-repair. I hope this battlegroup is buffed.

And hey since we're talking battlegroup/unit buffs, I don't have as much time to play the game or make forum posts, but I did want to say that MP40 grenadiers need a buff, they got left behind in the infantry TTK update and lose to almost everything. Hope they get some love too, and that we see some balance changes alongside the new battlegroup. Here's hoping it's not a heavy tank meta, though due to the current performance of the tiger I imagine it will be.