I've got 2 classes in the low teens and its pretty dull. It's also hilariously unbalanced. On routine they're pretty much all faceroll, except for the demon commander who can consistently fucking one shot you with an almost impossible to dodge attack. Then if you manage to survive that you still have to get out of range of his 5 second pbaoe terrify.
It's like Collectors in ME3 except you can't choose who you will fight in DAI.
The demon commander is one of the easier bosses if you have the right classes in the group. My friend and I consistently duo perilous with a keeper & elementalist, regardless of boss.
The damning thing about multiplayer that shows up after you figure everything out is that casters > everything. There is 0 reason to play anything other than a caster if you want to steamroll stuff, especially on perilous. Necros with Walking Bomb that spreads coupled with Death Siphon and the ghost mode passive (triggers on death) makes you basically unkillable, the elementalist has Death Siphon AND Barrier, which is crazy OP. Not to mention they all have gross targeted AE spells that you can use with other casters to abuse choke points.
If you've been pugging I can understand why it'd be not so fun. Especially with the gear curve in this game it can be pretty sad early on.
With that said, if you can manage to get a consistent group that aren't retards you can farm up the gold to start getting more gear and the game becomes easy. The upgraded armors for each class make a huge difference since armor is straight damage reduction. The same goes for weapons since all abilities & auto-attack are all based on weapon damage. For example the Arcane Warrior can get 30% of damage dealt back as a barrier, which makes you unkillable with a 140+ DPS staff, especially when you're using Vortex and the lightsaber to it's full effect.
At the top end you can solo routine on just about any character and threatening is no problem to carry 3 randoms and win. Once you have a good group you can do nothing but perilous and have staggered leveling (i.e.: two people with characters at 12+ and two people at level one) and you will be able to farm out prestige really fast. One perilous run for a level one takes you to level 10 iirc and if you're all playing casters, each prestige is +1 willpower.
TL;DR: play casters in MP and win. Demon commander loses to barrier everytime.