It's sad, but as Antag, I usually wait for 10 mins and lose... Simply, gid gud, though...
As of last night, at 60 difficulty with 4 stacks,
3 bombs for each tank and 6 x 4 Extractor in Short Fuse.
3~4 engineers constantly appear in Low Blow (It may take forever to reach the next phase..)
Weapon from the past: Adds become problem in the 1st phase if you do not take down the Drone fast. Luckily, Drone was not that tough. The rest seems ok, just watch for adds when the sphere's charge reaches max of each segment.
Hades AI become tanky (4 punches and 300~400 in shots) and hit you hard in Hanging by a Thread, but that was ok range. Engineers are pain in the ass at the final phase.
You may need Harec in Enemy within. I find Shae, Doldren, and most of 6th's members have hard time clearing demons when being chased by demons.
In the 2nd Watch Dog campaign map (ugly brains) was OK. I better have Shae in the team since Valeria's whip is not strong enough.
Double Agent was ok except Hades AI. Just clear them fast.
Overall, difficulty 60 is still ok with teammates, but I have difficulty raising my MMR to reach 70+ at this point. Also, there is no point raising MMR.
In soloQ, I rarely match at difficulty around 60, so I cannot do comparison yet. (Mostly I match with 2~3 newbies after 5~10 minutes. MSE tells me to carry them, but I'm ok with it.)