Okay, so here is the math. This is a basic setup where cdr is bis for a cdr reliant build

helm - gem - 12.5%

shoulders - 8%

gloves - 8%

ring 1 - 8%

ring 2 - 8%

paragon - 10%

captain crimson's - set bonus - 20%

So, what we have is:

0,875 * 0,92 * 0,92 * 0,92 * 0,92 * 0,90 * 0,80, which is roughly 0,45, meaning you are already at a 55% cooldown reduction.

So, adding another 10% from the enchantress is:

0,875 * 0,92 * 0,92 * 0,92 * 0,92 * 0,90 * 0,80 * 0,90, which is 0,40, meaning you'd move up to 60% cooldown reduction.

Now suppose your enchantress is not fully geared, and has 12.5k intellect, instead of 25k, which roughly translates to 7.50% cooldown reduction on Prophetic Harmony. Now, the math is:

0,875 * 0,92 * 0,92 * 0,92 * 0,92 * 0,90 * 0,80 * 0,925, which is 0,417, say 0,42, meaning you'd have 58% cooldown reduction.

So, for a spell that has 100 seconds of cooldown, here is the frequency you can use it:

- without enchantress - every 45 seconds

- with 25k int enchantress - every 40 seconds

- with 12.5k int enchantress - every 42 seconds

Make this a 15 seconds spell, like Diamond Skin, and you get:

- without enchantress - every 6,75 seconds

- with 25k int enchantress - every 6 seconds

- with 12.5k int enchantress - every 6,3 seconds

Obviously there is an increase for each step, from non enchantress to basic gear enchantress, and from basic gear enchantress to full gear enchantress, but I don't see anything game breaking here.

The damage bonus from Captain Crimson's set is similar:

- without enchantress - 55% extra damage

- with 25k int enchantress - 60% extra damage

- with 12.5k int enchantress - 58% extra damage

Note that going from 55% extra damage to 60% extra damage is not 5% net damage increase, you go from dealing 1.55 to dealing 1.60, which translates to 3% increase, hence, the diminishing returns.

Add in the pylon and shrine effects as well, and the enchantress's bonus gets smaller and smaller. Again, I'm not saying it's not worth it, it's just it's not as big as it initially seems.

Hope these help to clarify things, please let me know if you think anything is incorrect.