640 was pretty easy to get before Highmaul came out with war forged blues and the 680 ring

I agree with most of what you said, but this is just factually false. Before HM was available, Heroic WF Blues were still only 636 and the time-gated Challenge Mode pieces were 640. Aside from the ring, there were no pieces available over 640.

Even if someone had Heroic WF in 12/13 slots (assuming they have an OH and not one of several classes that do not) and a 680 ring in the last, they'd still only be 639.38 ilev. If they had instead just half 640 gear and half 630 gear, it would still be only 638.46 ilev. Hell, even if you remove all 630s from the equation, it still requires 2 slots of 640 with 10 slots of 636s to even reach an average of 640 flat. If you're unlucky enough to not roll any WF out of Heroics, it takes 8 640s to reach a 640 average iLev.

And bear in mind, CMs were not "easy" to do at that time. We had little to no understanding of the tips & tricks to each dungeon, we did not have CM-specialty gear available to scale down, most of the CM-strong BoEs were astronomically expensive (far out of price range for most people), and executing them required a full group if players with at least the skill to do Heroic raiding. Even getting ONE of those CM rewards was a feat for the average player. Add to that, you could just as easily open the cache and get a slot you already had filled (and obviously the more you get, the higher chance of this), so even if you had a solid team to do them with each day, it took weeks for even the early-starters to get close to 640.

So to suggest that getting 640+ was "easy" at the time just reveals that you didn't actually participate in that gear race, or don't understand the diminishing return of averages.

I'm not even much of a numbers guy, but this only took a couple very simple tables to see this.