Is there math out there for stats?

[StrejdaTom]

Sir, please state your question more clearly, so it can be answered.
Thanks.

EDIT:
Oh nvm, you have edited it (at first I was able to see only the first sentence of your thread).

Healing is better for healer, healing done is better for tank and dps.
20% increase in dps should be completely the same as 20% increase in mainstat, atleast theoretically and if we aren't talking about healers.
Skill speed and spell speed affect your cooldowns and skill casting time, attackspeed in my opinion affects only skill casting time, so skillspeed/spellspeed should be better.
Again, damage taken and defence increase should be on par.

People, correct me if I am wrong.

[Sevyrr]

Skill speed and spell speed affect your cooldowns and skill casting time, attackspeed in my opinion affects only skill casting time, so skillspeed/spellspeed should be better.

From my understanding of weaponskills and the effects of the Arrow buff via Astrologians, attack-speed effects the skill cooldown time, and not the skill cast time.
Experience of the Arrow as a Caster eludes me, so I can't say how it effects cast-times.
Skill- and spell-speed, however, effect both casting and cooldown times, although in a less direct manner: similar to how "accuracy" and "chance to hit" work, skill-and spell-speed are converted to a hidden, relative-to-level, "attack-speed" statistic, that determines the effects.
As such, a buff to attack-speed is a direct buff to that effect, and a buff to skill-/spell-speed buffs the relative gain. (IE:- Attack-speed buff has greater effect than Skill-/Spell-speed buff).