Suppressor Grenades are fine right now
Should prevent activation, not ongoing supers
First off, I think Suppressor Grenades are cool, and the following is just an opinion. If you don't agree, that's fine! Just try not be a jerk about it ;) I think Suppressors should prevent enemy players to ACTIVATE their super, but not shut it down. That's what the Nightstalker Tether is for. A super shutting down another super seems fair, don't you think? Some might think that if a granade doesn't shut down a super, than a snipe bullet shouldn't either. In my humble opinion, the nade is way easier. When I'm sniped out of my super, I applaud the guardian who shot. When I'm supressed out of my super I feel robbed. How bout you?
According to The Merriam-Webster Dictionary: suppress: vb.: 1. to put down by authority or force : SUBDUE. 2. to keep from being known; also: to stop the publication or circulation of. 3: to hold back : REPRESS. Currently, the grenade does 1 and 3 while tether does all (if suppressor grenades left residue then they would also do 2). What you are preposing is that they only do #3. However, then they would not be a suppressor grenade, they would be a restrainor grenade. Can't argue with facts and sound logic (or the person who's not afraid to grab telesto in crucible).
It's not really some super broken thing, nor do I see it ruin anything big. Most supers can even avoid being hit by these if the user is a quick thinker.
I think it makes total sense, but unfortunately people have a funky idea of balance.
Ever use a Titan?