Definitely not just flash. Hes just overused. Canary cold blue beetle have 50 50s that are just as messed up as his but how many actually use him? Hellboy leaps fullscreen and can put u in a 50 50. The only tame thing is lack of a run button. I personally feel like these 50 50s are on par with last patch mkx
It's not like Cold can just walk up and straight mix you though, he has to get the knockdown first. Hellboy, he does have mix, but it's not like it's free if he just does a fullscreen leap, if you're ready for it you'll anti-air him consistently. If he staggers it then it becomes harder tho.
To me the only true 50/50 characters are Bane, Canary, Beetle, Brainiac, Cheetah, Flash, Firestorm, Scarecrow, Swamp Thing. All other 50/50s require setups, are fuzzyable, or need some sort of special circumstance to be done. These are the only characters that when you're at negative frames it's a guess.
And Darkseid I guess. Maybe Hellboy.