Melee Crusader can pretty much play from level1 to the end with Greatsword and Greataxe (piercing). They also have minimum lvl requirements. I find all sword+board lacking and unsatisfying - at lvl15 Powerhammer is unlocked, and it can be used for killing bosses faster than Greataxe (armour breaking vs. piercing), and Suppression Shield helps in surviving them a bit - but, as I said, I find Greataxe better (also: usually Eviscerator later in the game, rather than Greatsword).

[EDIT]: Yes, lategame in killing 300+PL bosses, Powerhammer + shield become a must, because ultra-fast HPreg...

Psykers seem to fall apart as melee people at higher levels. I never switch in missions unless I'm way over the power limit. 

An inoculator with 2 heal spots ~10 charges, empyrean armor (timestop), inferno|holocaust, fiery form, precog shot (whatever it's called), and there's very few things you can't shred. My inoc gives me +10% dmg, fiery form is +50% heat/+20% normal dmg, +100% (for first shot) from precog shot. 

You hit precog shot, then fiery form. Witchfire to clear out the littles, timestop to pin the nurgnaught in place, while holocaust and the flame aura from fiery form chew him up. Suplemented with witchfire and warp rod shots. As soon as health gets down to around 60% inoc goes off. With holocaust, if you have your inoculator already going...you can just hold down the 'fire' button and it'll do as much damage as your health and warp heat soak will let you do. Still gotta run and break up large groups and not walk into ambushes.

Psykers are really really squishy. There's some levels in the teens where you either have to trudge through a lot of grey missions or get someone to help you over the hump. I still can't manage a timed mission or to not die in a relic tarot mission yet. (lvl 30 r/27 acct).

Psykers also seem to be weak against bigs. Russes and naughts. As far as I know, there's not really a 'good' build for psykers for taking out heavies. 

Psyker:

I can totally not agree that they are squishy, granted, the other two have one thing through attributes with 0.5% HP and SR regen, and the psyker only has the 0.5% regen through the skill trees, but psyker does generate a whole, whole lot more class resources than the other 2 combined.

I walked through tarot missions on "impossible", and it was far away from being impossible, was not exactly facerolling stuff but quite manageable.

Those timed missions from cabal, kill 300 in 5 minutes, I finished the first 3 I tried with 5, 6 and 7 mintues remaining respectively (you get more time added through kills, therefore you can go above the initial 5 minutes).

Some things are broken, bugged, or do not look like they work as described, but it's doable.

Sidenote: The perk "self flaggelation" (for grinding 5k fate) would be super OP for psykers but increases warp heat instead of lowering it. :D :D :D

Setup:

- dual warp rods, for the normal attack has already AE and lower CD than say a pyro-staff, witchfire adds nicely on top of this

- bio lighting as main dps spell with +dps, -CD and stun (for the rare situations where things last long enough to be a threat), the lower CD and increased effect (more warp heat cost) for generating more warp heat through it (yes I said more^^)

- fire form: more dps, more defense, simple really, also a nice button to generate a bunch of warp heat at once

- endurence: for taking less dmg, seems to not really add up with fire form, but lasts long and it helps

- divine shot: 100% more first hit dmg means any regular mob is a onehit, simple, very effective, saves a lot of time, try to hit bigger mobs with bio lighting first for best results

- death augury on 2nd weapon set (TAB)

Note: buffs (fire form, endurance, divine shot) with -CD and +duration ofc

Skill tree:

- 3 points in the lower right corner of the support skill tree for 0.5% heal per warp heat point gained!
This is a very, very important thing and will generate so much healing that you can keep your HP topped if you're not being totally reckless.
This is the main thing how this build works and what makes it keep going.

- points into more HP and less dmg taken help, too, also one point into that psyker skilltree for unlocking stun

- 4 or 5 points into movement speed, including 10% speed if not in combat, running faster saves a lot of time in the long run ^^

[edit:] there is one thing in the skilltree saying "inoculator goes off CD if you go below 20% HP", this also helps, a lot

Playstyle:

- buff up with death augury, divine shot and endurence, keep those up all the time

- regular mobs are onehits, dual warp rods help with AE, ofc try to place witchfire so that you hit the most mobs at once with it

- fire form is used to gain a bunch of warp heat at once, and against many melee mobs ofc and as additional dmg against tougher enemies

- non-regular mobs are facemelted with a combo of the warp rods attack + witchfire to remove warp heat, and bio lightning to gain warp heat, dealing serious damage while also healing at the same time, and as said before: recasting fire form can also add warp heat for the purpose of healing besides adding defense and damage

K.

Every Item if possible with hp per hit/sec. 

Armor with these two duplicates

2x Arc Blade (Main), second Arcsword or Boltpistols WITH hp per hit (depends on your playstyle, these BPs heal alot)

Incolator with dmgboast and crit

VoidShield as Backup (protects from gas in nurglemissions)

Took me easly to lvl 20 with lvls more then 100pts higher... Just have to stop to revive my coop. Dont know if this is intended but your copys do stundmg in this setup. Most elites are stunned after a few secs.