Maybe you shouldn't have included Legion in the list then lol? Just saying!
Legion started off appalling, like APPALLING OMG. And then it improved so much on this, that most people basically forgot it ever was appalling in the later patches. The AP catch was massive and rapid. The availability of legendaries steadily improved from "shite" to "okay I guess" to "just buy the one you want with this new currency" over the expansion. It did undeniably start out fucking horrible though.
It's an expansion where catch-up went from nothing (and was also really alt-unfriendly, because of the way it worked), to excellent.
As I recall, the cap was pretty low. However it worked out, it was largely worthless for me to run more than a couple of Heroics a week whilst raiding (which I usually did to help people or complete achievements). Also the pricing on the gear meant it was a very slow way to get geared IIRC.