So, here's my general notion for how party "roles" ought to work in this game (not that we exactly have those) as an aid to development aims. 4 degree scale, Poor -- Moderate -- Good -- Excellent:
Tank
Damage: **GOOD**
Damage Avoidance: Excellent
Damage Soak: Excellent
Healing/recovery: Moderate to Poor
CC/tactics: Moderate to Poor
Melee Dps
Damage: Excellent
Damage Avoidance: Good
Damage Soak: Good
Healing/Recovery: Moderate to Poor
CC/tactics: Good
Ranged DPS
Damage: Good
Damage Avoidance: Excellent (although about 50% of that is Because Ranged)
Damge Soak: Poor to Moderate
Healing/Recovery: Poor to Moderate
CC/Tactics: Poor to Moderate
CC/Heals
Damage: **MODERATE**
Damage Avoidance: Good
Damage Soak: Poor to Moderate
Healing/Recovery: Excellent
CC/Tactics: Excellent
Nor should this be Locked In, for instance there are Tank Healer builds that basically replace damage with heals. There are hybrid builds, that's fine, but there should be a solid starting range for "full focus" builds. But right now in most cases tanks don't get ANY dps and ranged CC/heals also don't get ANY dps, meaning that a lot of times you're running with a bunch of melee and ranged dps with NO HEALS/CC and NO TANK because THOSE BUILDS SUCK TO PLAY because their damage is nonexistent and it's getting annoying.
And, yes, I know it's very hard to boost those two build categories without *accidentally* boosting some DPS build into godhood.
IMO the best way to boost tanks and Ranged CC/Heals builds without boosting the other DPS builds is to give them some damage opportunities that slowly stack up over time. So their ability to stay alive (either by soaking damage or by outhealing it) means that they can gradually build up to maximum damage potential. Whereas focused DPS builds should be as front-loaded as possible. The build-up damage doesn't help them because by the time they'd build up any stacks everything is dead and they do so much damage anyway that on, say, a boss fight it's not worth the investment for them. But that damage increase for tanks and cc/heals builds pushes them from Poor damage to Moderate/Good and means that they CAN kill stuff if they have to.
Also keep in mind that there ain't no such animal as CC that works on everything in this game. Damage works on everything. CC is not equivalent to damage, it is equivalent to DAMAGE AVOIDANCE/SOAK. So you shouldn't be trading damage for damage avoidance soak or damage for CC, you should be trading heals/soak/avoidance for CC and vice versa. A tank should have reduced CC potential. CC should have reduced soak. Melee DPS trades some CC, some soak, and some avoidance for maximum damage.
Instant kills are a form of CC, not damage.