Group Viability.

I'm starting to get a feeling that Barbarians, Rangers, rogues and Chaotic mages isn't as wanted in groups as other classes because they don't have anything that benefits the group.

Hydromancer - got mana aura from the elemental,mana is never wrong to have, short time stun.
Paladin - Extremely wanted healer, with nice mana restore buff.
Druid - Good healer and tank, especially with the armor aura.
Cleric - Good support healer with extremely good buffs.
Arcanist- Nice aoe damage for huge packs - Needs better survivability soloing, never seen it played because everyone think it sucks.
Pyromancer - Nice aoe and a mana restore buff.
Warrior - Tank, who doesn't want one?
Chaotic Knight - Good tank with a small area heal.

Ranger - Wolf to offtank.
Chaotic Mage - same as above?
Rogue - ?
Barbarian - ?

Suggestions to make Chaotic Mage more viable in groups:

-Make the melee minions restore all nearby allies health by 1% of the damage they deal.
-Make the caster minions restore all nearby allies mana by 1% of the damage they deal(Would also make us use those more, currently everyone uses the melee ones as they are decent tanks when soloing)
Or
-Make life drain heal everyone near the chaotic mage by 50% of the health the chaotic mage gets.

Suggestions to make Ranger more viable in groups:

-When the ranger critically hits someone, it increases all damage the target take by 10%
Or
-The pet can get some growl that reduces enemies damage done.

Suggestions to make Rogue more viable in groups:

-Make some ability to reduce the targets chance to hit by some %
Or
-When the rogue critically hits someone, every ally nearby gets a buff that increases their chance to critically hit by 10% for 5seconds.

Suggestions to make Barbarian more viable in groups:

-Make the life steel go for the whole group.
Or
-Make the barbarians critical strikes make the group go into frenzy, increasing attack speed by 15%.

Those are all Extremely good single target dpsers, with many other possibilities, but they dont bring ANYTHING to the group, no buffs or any posetive effects.

I'm not saying they are bad, or needing a buff, since they are well balanced as it is. I'm just saying it would be nice if every class has some positive buffs or effects to bring to a group, especially as the bosses is getting harder.

It's like wow, if you dont give the raid anything, GTFO!

I always want a CM in my runs. Why? Because in Kyron when the adds come along, CM can take care of it easily. Ranger is dps and with their traps bosses may go down quicker. And their hail of arrows(Not sure if thats the correct name) can help take down creeps when they come in swarms. Idk bout Barb and Rogue. I never ask for these guys but if they come along then they are welcome.

This is just my opinions on the ones you call unuseful.

CM does great damage on boss fights and normal fights (except twins, the summons tend to die a lot). But as of right now CM is one of the most wanted classes due to the massive damage output by summons and decent spell dmg output by the CM himself. Also having a free way to deaggro tons of chasing mobs is also nice :O. Rangers do good damage and have that slight aoe, traps (stun very useful on murton), and a wolf to offtank as you said. Barb has the warcry which increases all other heroes' dmg, and barbs do really good damage to 1 target and have the slight aoe cleave too.
Rogues I have not experienced much from, they may be really good at single target damage but I have yet to see a rogue who doesnt sit in stealth 50% of the fights.

Barbarian with 15% increased attack speed is nuts. only thing about barbarian is his ability to survive by himself and not allways to be protected WHILE dealing great damage. Anyway Cleric would my prefered choice for a healer since he has usefull buffs decent single target heals and the best AOE heal and allso a tank buff. Paladins rarely reaches the same lvls of spell damage and intelect as clerics unless. VERY rarely

AH yes forgot to mention CM and barb both being able to fight without needing heals, and barb can even tank if needed (just put on a shield). Barb does it through high HP and then his lifesteal ability (I know it is not up 100% Of the time but still he can back out if he is taking hits and rarely needs a heal) and CM has summons he can use to meat shield and he has a 10+ second siphon life that for me at lvl 32 heals ~200 a tick. So both are great low-maintenance (healing and yelling wise) damage dealers with high damage, no reason not to take them in fact I would take them over a hydro or arc or ranger any day unless we have 0 aoe