Might I suggest using Detect Pots, Mage Light, Flare, and not being a full support build that's just asking to get ganked since you can't counter pressure?
When get attacked on my healers I switch bars and fight back to dump on my assailant. It doesn't always go the way I'd like, but it's a way better alternative to sitting there praying for a teammate to notice their healer getting slapped around.

Detect pots even free up a skill slot so you don't have to have a sorcery skill. That makes it even easier to slot flare or magelight.

I can't go within 30 meters of a guard looking the other way without getting yanked out. That's why there's no cooldown.

Players have more counters to shadowy than ever. That's why there's no cooldown.

It's expensive (even if you think otherwise). Even more expensive than mist form per second. There's why there's no cooldown.

Everyone in the game can crouch and sneak. The one big defense we have is shadowy disguide. That's why there's no cooldown.

Comparing it to streak isn't fair. If you streak 3 times you're gone. You can even hit an invisible pot to push it further. You've competely left the battlefield. Not to mention the other benefits on the two morphs on the tool tips.

Adding a cooldown or increasing cost to SD has the same effect. You kill NB dps in pvp. Brawlers cannot compete with templars and dks on average.

There has never been a point in this game where defenses against ONE class have been so easily attainable by everyone else, but people still complain.