I'm not sure that this play does constitute a tragedy for Malvolio, for if it were, he should come to some awareness and new understanding. Also, others should suffer or experience some negative consequence as a result of his actions, and none do.
Instead, he feels wrongly treated (he was) but does not seem to see how his own character traits set him up for this abuse.
He certainly has the right to feel sad, for Malvolio has most definitely been "notoriously abused"; even the audience giggles at his expense. He has been held up for ridicule, his personality is exaggerated (thanks to the ruse), and he is mocked to within an inch of his sanity. Beneath the humour, however, is an individual whose personality is such that he is found to be ridiculous, and that, for anyone, would be tragic.