Why doesn't pve have pvp combo structure?

[Achantion]

Shadowfang was a combo finisher like Armour Crush. It's now a standalone GCD skill.

That was just an example of how you could handle certain moves in a worst case scenario.
Ideally I'd stick 'em all in a combo, or one of button with cooldown.

If you actually consolidate NIN's combo skills, you save 2 buttons at most, but then NIN's rotation is 50% hitting 1-1-1-1-1-2-1-1-1-1-2 etc.

Do you really want DRG to be 1-1-1-1-1-1-2-2-2-2-2-2-1-1-1-1-1-1-2-2-2-2-2-2 with occasional Jumps?

It's indeed very convenient if you ignore oGCD's and combo's that could have been added instead in your examples. The whole idea is to create more combo's with a specific purpose instead of damage dumps.

See the following example:
1 = three hit basic damage combo
2 = two hit combo ending in a dot
3 = four hit combo ending in a resource stack (let's say 3) that can be spend on 4.
4 = Ability with cooldown that doesn't break combo
5 = random oGCD buff
6 = random oGCD group buff
7 = random oGCD attack with follow up attack
8 = Shadow fang like stand alone

3 - 5 -3 -3 - 3 - 4 - 8 - 7 - 7 - 2 - 6 - 2 - 1- 4 - 1 - 1 - 1 - 2 - 4 -2 - 5 - 4 - 3 - 3 - 8 etc..

Less buttons than most existing classes, yet more engaging because it has multiple things to do with different pre-requisites and other stuff.

Again, how do you accommodate for MNK's Perfect Balance, Form Shift or SAM's Meikyo Shisui?
[/I]

I don't see the issue here? These skills right now are needed because of the way the game is designed right now. Just adept these skills to work in the new system.

Meikyo Shisui as an example: You either use this skill to get your 3 sens (which are all combo finishers so there is no problem at all, as this could perfectly work in a consolidated approach) or to quickly refresh buffs. In case of the second option, just change the way skills are designed with the new system in mind. Easy fixes are to stick the buff in the combo finisher, create oGCD's for these buffs, or just live with it that you can't use Meikyo Shisui to achieve these, which is perfectly valid too.

You say consolidating buttons makes room for new skills, but then how long until you want those new skills consolidated and we're back where we started? After all, they all just deal damage.

Obviously not, if each "chain" is designed with an idea/mechanic in mind. You yourself suggested to combine skills like Ley Lines and Between the Lines, so you obviously understand some skills belong together.

On the other hand, it's easy to see skills like Vorpal Trust and Jump don't belong together, as Jump includes movement an animation lock, unlocks Mirage Dive, etc.. Meanwhile Vorpal Trust, True Trust and Full Trust are simple reskins of each other that work identical and only Full Trust serves a purpose, so nothing is lost consolidating these.