I think you're underestimating just how long the startup is...not to mention he's still in recovery well after it activates. Any Deathstroke using it straight up will get punished. He gets the most hard knockdown advantage from a Sword Flip after 1 popup so he can activate it then but...
Several characters can still punish him and be right in his face
ex. Batman's grappling hook, Killer Frost's slide, Ares' godsmack...
Other characters can punish it and run down the trait
ex. Sinestro's shackles, Grundy's swamp hands, Raven's soul grab thing...
In fact the only character that can't punish it is I think Bane and well I'm sure DS is fine in that matchup without it. Seriously the startup makes it a gimmick to catch people who are sleeping. The only other time to use it is to cut your combo short and D2 XX trait and that's silly. There's no other situation where it's safe. If someone can describe a situation to activate it and then actually capitalize I'm all ears.
I've actually used Deathstroke quite a bit I know how long the start up is. If the opponent is straight up dashing in you're not doing a good enough job of conditioning them after a knockdown. You're not supposed to be able to trait whenever you want and lul it out with unblockable shots. The trait is supposed to be difficult to set up because of how good it is.
Like i said off of a knockdown Stroke gets a free low gunshot every time. You condition them to wait for that and trait, hell you could even low gunshot, fake the frame trap high shot and go into trait. I also mentioned previously it should only be used in certain situations. You should not be using it against Superman especially if he has full meter lol, as well as some others.
Also lets say you do trait, get it activated and Grundy swamp hands you, he dashes in to pressure. You wake up DB3 MB into the low, it connects. You get a hard knockdown and a free j. 3 cross over, it's blocked your traits stil up you can get a free 132 unblockable combo.
Trait makes them think, sure on paper anyone can punish, but thats why its you're job to condition. If someone can easily punish trait it's one of two things a) you're fault for not conditioning b) you did it point blank wtf are you doing.
Say you do a low gunshot, delay MB it and it hits. You have no meter left and he has like 15% left. Gonna take awhile to chip him out he'll be in by then. Obviously you get another free low gunshot, but instead you trait, and win the round. You have to use it sparingly and wisely it is not some braindead trait (it shouldn't be either it's unblockable projectiles on a strong zoned lol)