The fact that there’s only three slots to play with means each of the three items in your loadout need to be doing some real work for you to earn its place, and CC gear certainly doesn’t measure up. The percentages and cost of anti-CC gear seem to be running on the same numbers as other gear like attack speed and attack damage, but the difference +15% damage or +15% attack speed makes to a character compared to -15% stun duration is night-and-day.
Considering most CC lasts 1.5 to 2 seconds, slicing a fifth of a second off won’t even be perceptible the majority of the time. If it was more in the region of 25-30% CC reduction as a primary stat with a 10-15% showing up as secondary, I might consider dedicating one of my precious, precious loadout slots to it, 'cause a 40% reduction would actually make a tangible difference. But even then it would still be competing for space with constant benefits like 15% attack damage or +400 hit points, and its inclusion would still depend on the character I’m gearing up.