Please correct me if I'm wrong

Aal, description is "Increase Skill Damage" by the percentage of Aal you have.

-An additional constant damage per hit/multiplier is applied to a skill that uses Aal.

Ahib, description is "Chance of Extra damage"

-Description suggests "extra" damage, it will only apply once every skill. Extra damage is equivalent to the base damage of the skill(without the multipliers), applied as last hit.

Labreve, description is "Increase Skill Crit Chance"

-As we noticed, crit can be applied in every hit or multiplier shown in the Damage Rates display. Labreve crit chance is only applied to the skill that uses it.

 

Serrett, description is "Increase Number of Targets"

-Increases the number of targets affected by a certain skill, may it be CC, Damage, Debuff, Buff, or Heal.

Kinda wish it was like you think it is.
But branch and percent on branch are two separate things.
There's many precise guides, just see most popular YT creators.

Deleted by the writer.

So I did some tests after reading your reply.

Branch Percentages are just fixed additional damage to the skills. 

While Branches themselves have their own bonuses.

 

Aal already has a constant damage at around 10% excluding the percentage of Aal you have.

 

Ahib really deals almost the exact same amount of your skill's damage, but the chance to proc Ahib is not based on how much Ahib percentage you have. 

After some tests it takes 8 to 9 recasts to proc Ahib. Which can be concluded Ahib proc chance is also only around 10%. Which can only proc once every skill. And the Ahib percentage you have is just an additional skill damage. 

 

Labreve also only has around 10% of fixed increase crit chance for that skill. While your Labreve percentage is just an additional damage. 

 

While Serrett only increases 1 target affected. And the percentage you have is just an additional damage for that skill. 

 

So overall:

Ahib is good for 1 shot 1 multiplier skills. But needs good RNG.

Aal is the best branch since the 10% increase damage it grants is constant and not RNG based.

Labreve is sure is good for multiple hits/multiplier skills since it gives more chances to proc crits.

Serrett is good for Healers and Disruptors in large skill PvP. Though Serrett needs at least 1 more target affected.

 

thanks for that.

 

And after knowing this, I hope PA would allow ovecapping substats with the use of Skill Enhancements. And let us freely choose what type of substat skill enhancement we would want to add for that specific skill.

Kinda better xD but some still wrong.
You'll find out while gaming ;P
Just use what you see working, mostly quick skill, but affecting target with statuses (stun, knockout, lower speed, etc.), and yourself with buffs (hp recovery).
Also don't always have to use all eight skillslots with different skills.
Me farming use five skills only (to stand in spot, in crowded areas -not attacking others players),, in pvp like arena 1vs1 I'm using FOUR only (just because it's comfy), and multi-pvp all skills. But it's only me.
You'll get to know )