And that's still asuming the Goblins bunch up in just the right formation for a cone spell to hit them.
Well, if you're fighting 26 goblins in anything other than a flat, featureless environment, it's pretty hard for them not to bunch up.
On topic: I just simulated two encounters between six 2nd-level Fighters on one side, and 2 wights, 8 zombies, and 12 skeletons on the other (which I thought was a Tough encounter, but read on).
In the first, I had the monsters evenly spread their attacks among the Fighters, and the wights didn't show up until after the zombies were dead. The Fighters took several rounds killing the zombies, then mopped up the skeletons while dealing with the wights. They suffered 2 fatalities (if they had a war cleric, they would have been fine).
In the second, I had the monsters focus fire. The first Fighter died in the first round, and I didn't need to continue any further.
Then I realized I had misread my note: it was supposed to be 12 zombies and 8 skeletons, not the other way around. Skeletons are worth more XP than zombies--which is clearly stupid, since literally any hit with a blunt weapon instantly kills a skeleton, but zombies never ever ****ing die.
So... I dunno.