Is it really only 20%?
Theoretically on a good day, yes.
For me most of the time it’s a big fat goose egg. 
are any opponents crits only what the game says they are? my dinos rarely ever crit but i get crit against so hard.
There’s a fair bit of luck involved with RNG
My Monostegotop has never crit in an arena battle, same with my Allosinosaurus.
I still keep the faith that someday they will, it’s just a matter of chance
Allosinosaurus never crits for me. I took it off my team cause it dies much more than it kills
It’s the one stat among all dinos that stands out repeatedly when Im battling - I seem to get crit by MST far more than 1 in 5 on a consistent basis.
My mono crits but usually when I would’ve killed the Dino anyway. Oh the dinosaur is low health let’s Crit for good measure.
Ive noticed if it crits once, it crits twice.