IMO, i think shadow swap is good as it is now . having the ability to choose the squishiest player and swapping with him into your territory is really .. >.> i'd probably hate you (DA) if i were that squishy player .
but anyway, so yeah, shadow swap can also be used as a life saver, a getting out of trouble skill.
a life saver in a way that you can swap with an enemy dg whos about to kill your teammate .
i don't have to explain how it can get you out of trouble do i ?
so yeah .. besides, whats the point of reducing mana and armour when you are not teleporting to him, you are swapping position with him . but the time you get back to hit him, you can probably land 1 or 2 hits before the armour debuff finishes .
similarly for the speed reduction . warp strike has a bigger range if im not wrong . just use warp strike to catch after him and finish him with a spine attack (if you have it). you cannot disagree that spine attack is a wonderful finisher 
p.s. do give me some criticisms on my opinion . i'm still trying to improve . 