Well the enemies that spawn at the end of behests are usually larger than normal...but if we cant have beast tribe enemy bosses that lead stray monsters to cause havoc around the place, at least make the last behest enemy once of the more menacing monsters with a larger size:

Ahriman
Drake
Boar
Gobbue
Salamander
Diremite (horned scorpion class)
Malboro

As for monster variation, I agree. We should be seeing non-native enemies to the region invading, especially if behest is to knock out hordes of enemies causing more trouble than usual. Should be encountering things like flan,antlings,diremites (i just like their design lol), Piestes, etc.