Cole always warms the bench at Skyhold in my games because Sera just kicks so much ass and he dies so easily on Nightmare. And his banter is a little weird. He starts up conversations about things that people don't want to talk about. It's really awkward and I don't like it. I like Cole but his banter is weird.
In my previous playthrough (Hard level, DW Rogue) I never used Cole. The AI for melee DPS in DAI is awful! They don't understand that...well...if you have a big guy swinging a huge axe, the safest place to attack it is from behind. Even Iron Bull was eating dust too frequently as huge as he is. In the fight with the Envy Demon (Templar quest) Cole died at the first hit and was sleeping peacefully the whole fight! So my team was Cassandra as Tank (most of the game her gear allowed her health to cap when out of combat), Varric as crowd control, Solas as support/barriers/dps/rezzes and my DW rogue mincing things.
This time around (Nightmare) I am playing an archer, my team is quite bizarre but oddly works like a charm. I have Blackwall as Tank, picking the hard hitters, Cass as offtank picking the weaker ones, Vivienne (so far with spirit tree, but once she gets the Knight Enchanter tree, she will be using it, they seem to have a lot of survivavility) and my guy as far as possible from the whole action.
My "secret" (if any) to finish the Insanity PT in ME3 as infiltrator was pretty much the same, my team role was to act as "bait" to keep the mobs away from me while I was tearing them down with the sniper rifle at a safe distance.