Cross class abilities never made you the equivalent of what you think of as multi-classes in D&D. You didn't get the ability to use all of the Monks toolkit as a Bard, for example, and couldn't fully use the Bard's toolkit as a Black Mage.

Cross class abilities didn't really add 'flavor', as most of the abilities were extremely low-level by the time Heavensward came out. Truth be told, all of the Good abilities you got from cross class are encapsulated in the current Role abilities you get.

It also felt weird that you couldn't advance as a Bard unless you took the two required cross-classes to level 15. There was a decided pause in your gameplay while you attempted to learn a new class simply because the game required it, not because the benefits outweighed the disadvantages. It was a relic of 1.0, and SE removed it when the second expansion came out, if memory serves.

The unique part of FFXIV is that a single character can take on more than one job. My Warrior of Light can be both Bard and White Mage, Warrior and Ninja. RIFT did something like that by switching out Souls.

In WoW this was impossible, and the reason that I maxed out on the number characters on both Alliance and Horde side on two different worlds. If I wanted to play a Night Elf Hunter, I logged in as a Night Elf Hunter. If I wanted to play as a Blood Elf Death Knight, I logged in as a Blood Elf Death Knight. (To be fair, I had one character for each class on both sides of the aisle back then).