Essence Reaver was for mana sustain
Correct me if I'm wrong but the only reason I bought it was to cast as many spells as possible without having to back for mana. Now it does less of that while depleting mana as fast as possible. Sure it allows for some plays now but was that even the point of it? I mean 1% missing mana regen per aa means you're going to have to shoot about 6-7 times (maybe more) to cast a single ability.
Let's take Ashe for example, I'd buy Essence Reaver on Ashe to cast W and Q a lot and have that 40% cdr to have her ult up whenever I needed. Now the champion I'm definitely buying it on is Kai'sa, and Kai'sa doesn't even care about mana sustain.
I didn't buy
to cast all my abilities in 8 seconds, I bought so I can Keep casting those abilities.