I did a poll on this a while back in the reddit forum and was advised to bring it here after I brought up the idea again.
Realism in a game like this is impossible but lets face facts. If an 8 ft mandibled alien came at any human being with a sharp object, they would not whip out a knife and go “En Garde! Rapscallion!” You would dive, roll, run as far away as possible.
I think a dive mechanic would be a good replacement for parry. You see a combistick you dive out of the way. Adjust hit boxes so that the combistick misses low (downed hit box while diving?).
It fits right, gets rid of the unbelievable stun, and is also multi purpose. Oh plasma caster sight? Dive. Arrow just missed me? Dive. Predator rushing me? Dive out of the way.
Predator long claiming my teammate? Stab to death with a knife. First objective and we’re stealth? Knife the AI.
Just my thoughts