i am having this exact same same problem.
I am on xbox and have played many personal servers through nitrado and set them up to be the same as official with difficulty and the dinos have always been from 15 - 150. I have just started a new extinction server with the exact same setting as all my other servers and im getting dinos from 5 - 150 with 80% or so all under level 60. Very rare to find dinos over 130 and have only found one megatherium at lvl 150. Very frustrating.I have contacted nitrado but they say its not an isuue wi them.
I purchased another server hoping it was a bug with the one i bought but noits still the same. I then changed a crystal isles server ihad that was woring perfectly fine and changed it to extinction and still had the same problem.Not sure what to do about it or what the problem could be.
Are there others that have had this problem that might have any answers or fixes, would really appreciate any help.