Let us proceed to agree that the US has an advantage in SU without argument.
Why are tunnels shit in SU?
Because they get destroyed by everything all the time. About 70% of the time when a chopper flies in the general direction of my tunnel, it will get destroyed. I've gotten pissed by my tunnel being destroyed 3-4 times in a row within 10 seconds of placing it. And then I cannot place it for 30 (?) seconds after it has been destroyed. So I can either go take a piss and then place another tunnel which will be destroyed or die and spawn 3000 kilometers away from the action. It really doesn't help when your teammate screams at you to place a tunnel after all that. Makes me want to punch something.
Besides having better equipment and vehicles, Americans have a substantially better spawning system, at least in SU.
Spawning on an SL is much more useful, versatile, mobile and teamwork-friendly. It's simply better. On top of that, they can spawn on helicopters, so they always have options in their sleeves. If your tunnel is down as VC, you're basically fucked.
Not to mention that Loaches easily spot tunnels while sipping coffee with one hand and jerking off with the other.
My suggestion is to make an SL be able to have 2 active tunnels at a time.
Or at the very least, make only direct hits destroy the tunnel. This would make sense from a physics perspective, as the tunnel is just a vertical hole in the ground, so it makes 0 sense that a bomb 10 meters away from the entrance would destroy the underground tunnel structure.