I-Rex beats Monostegotops into the ground on even levels, without Mono criting which had only 20% chance of happening anyway, which isn’t even reliable. Indominus can also beat Suchatartarsauce easily as well.
Monomimus or Proceratomimus vs Indom is blind luck based, can go either way, depending on who dodges on which turn and how good you are reading your opponent.
The only dinosaurs with nullifying that beat her no matter what are Tanycolagreus, Magnapyrritor and Tyrannolophosaurus can only be beaten if the stars align for Indominus (needs both dodging and not being crit once)
Failing both dodges has a statistical chance of 25%, which is the same as failing a crucial stun. 25% chance of losing against 75% winning high tier dinosaurs like Utarinex, Diloracheirus, Tenontorex, Spinachsuchus, etc is more than worth it. It also has a pure 50% chance of winning both Indoraptor, and Erlidominus as well as Thoradolosaurus, which is huge as well.
The only uniques that win over I-Rex no matter what are only Trykosaurus (because it’s stupid anyway), Magnapyrritor, the latter almost noone utilises.
I forgot the name of the dude, but there is someone in the top 50 with an Indominus as well and he does really well with his.
Not to mention, I-Rex is way more than just dodging, the armor piercing big attacks and the immunity with almost tank level of hp can be used for some pretty hefty comebacks. I-Rex is only a gambling liability if you use it like one.