Currently, there are some services compositions that have different storage capacities between factions.
These are:
Ammunition Supply Point (US: 2100, USSR: 1100) (soviet -1000)
Heavy Vehicle Maintenance Point (US: 600, USSR: 1000) (soviet +400)
Helipad (US: 300, USSR: 200) (soviet -100)
Field Hospital (US: 300, USSR: 600) (soviet +300)
Living Quarters (large) (US 500, USSR 900) (soviet +400)
While these do balance out with 8300 supplies per base with 1 of each composition including 1 supply depot, it should be noted that Ammunition Supply Point and Field Hospital are only unlocked at Corporal, and the Helipad and Living Quarters (large) at Sergeant. This means that currently at the beginning of a round where everyone is a Pvt, the max storage you can build with only 1 of each composition you can build is 5100 for the US and 5500 for USSR, and at corporal it flips with US having 7500 and USSR only 7200. At Sgt is evens out to 8300 each.
Of course you can build more than one of each, but aside from the supply depot and maybe the arsenal, building additional services takes up too much space for too little supply storage. I think it would help if these compositions' supply storage capacities were evened out between the teams.
I'd also say I fully understand the game doesn't have to be balanced and differences between factions will occur, but then maybe the costs of these compositions should reflect how much they can store. With the US arsenal storing 2100 and soviet one only 1100, maybe it should be cheaper to build?
Here's an official article that provides some constants. If there are any differences in the game, it's likely a bug.
Maybe we could split the ticket into several parts?
Some would be dedicated to bugs, like in the example with the USSR arsenal, while others would contain suggestions for the cost of a composition depending on its capacity.
But the field hospital right next to it seems to merge the supplies and shows 2700/2700 (which would be the 2100 ammo supply point + 600 field hospital)... So it does store 2100 but doesn't show it properly?
So my initial testing was on a local hosted HQC mode with the MOB located at Crag Point near Corsair's Cove (south-east) with lots of uneven terrain, and with one of each compositions it did actually lead to the base having a maximum of 8300 supplies, but testing it again now at other MOB locations, it does come out to 9300, meaning there was 1000 lost in the arsenal somehow (perhaps because of the uneven terrain? or because everything had to be crammed in tight and supply points started merging?). Will update if I manage to reproduce this.
So in fact the limits per faction per rank, assuming 1 of each compositions. Would have to look at the default loadouts cost to judge whether it makes sense for soviets to get extra supply storage.
Currently, this report should be mainly considered a report on that the soviet ammunition supply point sometimes shows just 1100 supplies capacity and the US one sometimes shows 1000 supply capacity when they're built next to other supply storages like the command post, even though they actually store the expected 2100 supplies. I can't edit the original post anymore since it was changed to awaiting internal testing.
^ Pic 1: 2 ammo supply points, one near the command post and 1 away from it
^ Pic 2: the ammo supply point nex to the command post showing 1000 capacity
^ Pic 3: the other ammo supply point away from other compositions showing 2100 capacity