I would probably describe the platypus more as "nonsensical" or maybe "surreal" than "stupid," but that doesn't exactly negate your point (and it's not intended to).Oh, I agree that evolutionary history is the reason for the classes as they are, that just doesn't make me like it any more.
It's like how I'm sure there's a good evolutionary reason for a platypus to be an egg-laying, duck-billed mammal; that doesn't change that it's a stupid, stupid animal.