>ehm DK wasn't dumb, just stubborn
Donkey Kong is so stupid he couldn't be hypnotized by the tiki dude in the Returns intro -the implication being he has no thoughts (he has no grace).
Bear in mind, said tiki dude had successfully hypnotized a quadrupedal elephant and giraffe moments before. DK is canonically dumber than less anthropomorphized animals.
He was dumb as fuck in Mario vs. Donkey Kong too. Anyone saying he hasn't always been a big dumb monkey is telling on themselves.