Not to add to any sort of giant chorus of people saying it, but I do think it's a very, very weird choice to have such an offensive-themed support set with a high emphasis on location [T]AoEs...and still be incredibly, absolutely incapable of taking any mez. As mentioned by Awilix, it lacks any sort of panic response, any sort of ability that helps in survivability (besides the heal), and leaves the entire set feeling fun, but feeling just a couple puzzle pieces from complete (IMO.)
Overall, my suggestions on the set is to give it some more "chaos" to the offensive aspects (More knockdowns! Please. It has no survivability outside of buffing smashing and fire resists, one of which being a particularly uncommon damage type to find in most places, and the max HP is on a base 4 minute cooldown. This works great for other sets like Nature, but nature provides...a lot more buffs and healing. It's very hard to keep yourself alive. Also, the defense is okay to have, but it's the only source of defense in the set, and provides about as much as weave while forcing you to decide between slotting set bonuses for defense, or set bonuses for healing/absorb. The regen buff is great, though! ). My personal idea on mez protection was my thought process on keeping it offensive, but granting it some measure of survivability against being held. Thought of Fulcrum shift, and how it applies a buff to everyone around you and the targeted enemy,
Why couldn't Whitecap do the same, but with mez protection? Making it a LAoE would be nice, but keeping it targeted to make this simpler would be okay, too. Thought process is that Whitecap could grant you moderate mez protection (Maybe 5? enough to keep you from being mezlocked by anything that isn't dedicated to locking down everything), but have the potential to stack it twice on teammates (for a total of 10, middle-ground for typical mez prot in support sets).
Other than that, the set's a lot of fun! Needs a few wrinkles ironed out, but shows promise as a powerful team amplifier and fun as heck, to boot.