This is nothing personal, but it has to be said... both to you and to everyone else who I've seen do this... because it really does seem like it's everyone:
now that that's over with...
the main idea is to catch them off-guard... for the most part, he can sneak up on some of them... if not that, then he has gadgets that can either help him in a fight, or help in executing that specific method...
Flash may not see the bullet coming... and thus not move fast enough to dodge it
Wonder Woman does necessarily need to be injected in the ear... a small drone could easily be guided into her ear canal... etc
Superman, again, may not see the kryptonite, and Batman doesn't really need to take it out of the belt... just expose Superman to it to weaken him, and then do whatever after that
GL, could theoretically be hypnotized if he wasn't expecting it... plus I would expect it to be some kind of neural interface, not the "hey dude, look at this watch... now you're getting sleepy"
I suppose IF they were setting up a movie tie in show where they can elaborate on some things or add something that would contribute to the movieverse, then it would have more weight to it... as it stands, I don't see it working... and it just seems like Marvel are cashing in on the Avengers movies... so the actual effort they put into it would be questionable
DC don't put any of their characters out there... all we seem to be getting is Superman and Batman movies, while Marvel have had the Avengers, Spider-Man, Fantastic Four and X-Men... with some of the Marvel Knights... so pretty much every branch of the Marvel U is accounted for
Plus IMO Marvel have more relatable characters than DC