Hi I was just wondering why the rampant mod doesn’t effect these creatures as they fall off completely and become kinda useless?

This is not true. It does not change their characteristics, but controls their behavior. They are becoming quite dangerous
Perhaps the AI ​​on the Gleba is still in truce mode. By default, this is the first 2 hours, plus the evolution should be higher than 20%

ahh okay ive got big monsters in my mod list atm so i'm getting them on nauvis and there stats arn't getting changed at 1.0 evolution was just wondering if thats intentional as they've fallen off compared to the biters and that?

Big Monsters - Rampant does not affect this mod. Monsters appear out of "nowhere", including right on your base. If they appear far from your base, they go straight ahead. They can afford it because of the attack range of 70+.