Is Darda Goldenchief supposed to friendly with Muursat?

I was doing Ice Caves of Sorrow, and as the wiki suggests, after rescuing Evennia I just kind of stepped out of the tunnel, let the two groups of Muursat Elementalists begin moving, and then waited for them to go past.

The wiki said they would be taken down by the dwarven catapults and clear out some enemies along the way, but that didn't pan out.
Instead the Muursat only lost 4 or 5 to the catapults, and when the remaining Muursat reached the second-to-last boss they just milled about--the two groups wouldn't even fight each other. I had no choice so I tried to get through, but they turned my team into paste in about 10 seconds.

Is this normal behavior?
Is it just better to race ahead of the Muursat and try to smash my way through the Stone Summit? Though I'm not sure if I can kill them quickly enough, especially Goldenchief since he's a healer.

It's a glitch, simply because their AI doesn't progress any further than that. It also means that the dwarf's AI doesn't recognize them as enemies either. At that point you're toast.

Normal mode or hard mode?
After the hard mode update at the start of the year, the catapults no longer do enough damage to kill the Mursaat due to their increased HP in hard mode.

But you can still easily kill them even without an uber team set-up using simple Divide & Conquer tactics.

You can wait till the area where the road forks (and the groups split up), wait for a catapult to hit them, then aggro them back over the catapult area to get them hit again, then polish up the survivors.

Then rinse and repeat on the other Mursaat group further down the line, at the next catapult spot.

Also, it should go without saying, that you should make sure you are infused.