I play DT solo and do weeklies on 8 chars as of right now. I both enjoy playing different builds/characters and prefer to have an optimal, fun build for each one. Primary difficulty is Auric, though had to scale down to Damnation sometimes to try to get no-deaths runs, which of course does not guarantee that as Damnation has the challenge of less experienced players there.

Aurics can be punishing for many (and some of my builds) and thus someone manages to get nuked. New event can be fun, but often people do not have tools to properly deal with groups of carapace or forget that there are disablers or hordes. Teamplay sometimes is another aspect that just disappears.

My general observations on personal difficulty rating for the predominant builds I used:

- Psyker is obviously the toughest to play in such environment, very squishy, some teamplay dependability, cannot do everything on his own and carry the game if everyone manages to get themselves deleted. Great at clearing hordes, overall team support, removing some dodgy specials.
I use Deimos/Inferno staff, Brain rupture, Telekine dome, CDR aura and no keystone as I went for other utility talents.

- The second from the bottom would be veteran, my favourite class. Reasonably squishy, too, even with toughness damage reduction nodes. I'm absolutely comfortable playing the class and enjoy being the special/elite sniper, but do not feel that I can handle every situation solo either.
Use Chainsword 13/Zarona revolver, Krak nade, Survivalist aura, Voice of Command and no keystone for better utility.

- Zealot is my middle ground. Agile, very capable solo and brings good control/support. Have survived tough situations solo, saved the team. Enjoy the class quite a lot.
Use Combat Blade 3/Flamer with Blades of Faith, Benediction aura, Chorus and Blazing Piety keystone.

- Arbitrator is definitely quite easy to manage and be efficient with less effort than on the previous classes. Very capable all rounder, carried teams in tough situations with reasonable ease.
Use Arbites Shock Maul/Exaction 8 with Voltaic Shock mine, Reload speed aura, Lone Wolf, Castigator Stance and Execution Order keystone. Even with the non-working nodes I get the free marks and can react much better to the threats.

- Ogryn. Almost brain dead easy and quite efficient at disrupting and surviving anything the game throws at you. Super tough, not so agile though, so have to be mindful with dodges. Can push through almost anything, while crowd controlling and dealing solid damage. I had almost no solo-play situations because everything is on the floor most of the time and nobody dies.
Use Bully Club 3/Rumbler with Frag Bomb, Loyal Protector, toughness replenishment aura and Feel No Pain keystone.

Essentially this is a subjective ease of use/efficiency rating for the classes that I experienced during these few weeks since I got back to DT. It's predominantly from aurics and solo-play.

Eventually will start doing havocs more. My highest rank was 27 with randoms with average effort and low time spent in that mode. Reached it on vet and tried playing arbites in havoc - felt comfortable with both, but I suppose I would prefer playing veteran. I would not enjoy taking my psyker or zealot though. Ogryn would be possible.

And the bottomline would be that this is just an observation, not calling for a nerf or saying that, because I do not feel that comfortable on psyker or know zealot as well as veteran, they are somehow worse.