Depends on the actual teamfight.
If Team A managed to lock down Ahri/Lucian and burst them before they can do shit, then it goes to A.
With the amount of AoE hard CC team A has, thats not hard. Lucian is a terrible tank killer, so it's up to Jax to take down Nasus. With Teemo's blind and Jax's counterstrike, they should be able to do that without much difficulty. Trist and Lux don't have enough AoE to kill Jax (and Trist is one of the weakest ad carries damage wise), especially with Jax dodge, and since Lux will be focusing Lucian/Ahri.
if Ahri is a god with her ult and dodge practically everything, kill Lux or Trist and not die while they're at it, then it pretty much goes to Team B as long as Jax doesn't die before he can take out Nasus. Assuming Amumu and Nami already blew their major cooldowns, Luci and Thresh should be able to 2v3 Trist/Nami/Amumu since they just don't have enough damage.
If Thresh lands a halfway decent hook, Ahri and Lucian will instantaneously melt that target if it's a squishy. Just hope he doesn't grab Nasus or Amumu and Flay him into the rest of the team.
Generally this is how I'd depict it:
Amumu lands Q on Teemo, Teemo is blown up but all of Lux's CD's are used.
During this, Ahri ult's in and kills Lux.
Nasus throws Wither on Ahri, but Ahri has enough mobility and Trist and Nami not fast enough cc to stop her. Amumu is too far away and has just used his Q cd.
Nami ults to engage (not great, but they have nothing else and no substantial poke). Ult hits everyone except Ahri who is out of the fight for now (cd's and no ult, and also out of position from flanking to kill Lux.) Nasus and Amumu ride the waves into Team B, depending how far away they are Jax either jumps in and starts hammering Nasus or Amumu gets a 3 man ulti.
Thresh goes for the hook on Trist, prob hits since Trist isn't really expecting it (also her positioning sucks).
Lucian melts Trist.
Jax fights Nasus (Amumu is spent, basically nothing left). Jax seems to be winning but a Nami bubble will hit him (he's not moving much, just trying to hit the big dog), depending on stacks of Nasus (I'm assuming low, since you said he does low damage) Jax either dies or is just briefly cc'd.
Jax kills Nasus, Lucian advances to take out Nami, Amumu tries to stop him but is 1: blocked by Thresh and 2: Not enough damage/cc. Jax moves onto the closest target (his q is prob off cd by now), takes out whoever he kills (how long it takes depends on the target, but he does it).
So I think Team B would win since they need less coordination.