Shadowfang was a combo finisher like Armour Crush. It's now a standalone GCD skill.
It's been removed from the combo but it hasn't resulted in any button consolidation at all.
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?

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

"Pressing a button is pressing a button. Pressing 1 is the same as pressing 2 to me. It's the effect on the button that matters, if I press 1 and deal damage and press 2 and get a shield, THAT feels different to me. If I press 1 and do damage, and press 2 and do damage, how is that different from pressing 1 twice?"
90% of any given DPS jobs skillset basically just deals damage. I'm sure you're not saying 90% of their kit could be replaced with 1 button...

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.