Its most of the time like that...

Beast 2 levels above character level or higher -> hardly able to kill, causes huge damage, hardly a chance, huge experience
Beast 4-5 level below character level -> beast does no more damage, one gets hardly any experience

so its kinda needed to do lots of sidequests...i dunno whether its possible to do the mainquet without much sidequesting.. i did all the sidequests i could and still had problems with some fights...