Yes, Essence Reaver as an item is a really good option for CdR right now. And its intended users are Marks(wo)men/ADCs, the class of champions that are brought to teams for their high sustained damage.
However, look what reduced cooldowns primarily do for its intended users. Cooldown reduction is a tool to increase the frequency with which abilities can be used.
For an ADC, reduced cooldowns directly play into their strength - to bring sustained damage. The spells of the ADCs that build ER are, first and foremost, used as damage tools, with a bit of secondary utility added. On the other hand, look who does not build ER of the ADCs -
and
, all of which have spells with long range and significant utility, but rely on their auto-attacks too much to not go for the increased auto damage
provides. Ashe in particular is worth mentioning here - her Q was changed in the ADC update, with the (intended?) side effect of making ER less useful for her.
And that is exactly the point of ER in the new ADC itemization: It offers a diverting path between increasing DPS through auto-attacks (
and abilities (
).
On other classes, reduced cooldowns have a way broader scope of effects than just increasing DPS. A specific point to add here is that, despite getting reduced cooldowns, ADCs are still required to get and stay close to their targets to deal their damage, opening them up for a counter-attack. Even Ezreal and Corki, the longest-range of the ER users, are still required to get close to do more than poke damage.
Contrast that with what CdR means on a long-ranged spellcaster like Xerath or Ziggs. Reduced cooldowns for those guys mean that they throw out their rotations with a higher frequency, while staying at a safe distance.
EDIT:
Another thing: Magic damage dealers intended for sustained damage don't need much, if any, CdR, or are/were rewarded for building the stat.
: His two main sustained damage tools do not benefit from CdR much. One already has a 1 second CD, while the other is a toggle.
: CdR in kit.
: CdR in kit.
: Used to be rewarded with extra AS for building CdR. This made him spike too early, for which it was changed. However, he still does not rely on CdR as much for his sustained damage, but on AS.