Do you remember how the Mahabharata ends? The pandavas climb the ? (can't remember the name) mountain, and each one dies in turn. Yudhistra asks why, and a litany of crimes and misdeeds is read out. Finally, it is Yudhistra and a dog alone, and Yudhistra also dies. His biggest crime - gambling. Only the dog (Vishnu, if I remember correctly) manages to reach the top. They all ultimately ascend to 'heaven' but not before paying their dues. All were flawed.
The beauty of Mahabharata, apart from the prose, is in fact the fallibility of its characters. The foibles were created so that the common man/woman can identify with the characters, and learn lessons on how to overcome their weaknesses.
I guess you're thinking of the Mahabharata as myth. Vyasadeva wrote it as a history. Literal truth, which is how I read it. The faults of the Pandavas were so minor, so trifling, that their falling at the end was to instruct us to correct out own lives.
Krishna told Arjuna on the battlefield that he had godly character (15th chapter Bhagavad Gita). And that He (Krishna) and Arjuna had taken birth many times in the past; that Arjuna is the eternally liberated companion of Bhagavan Krishna.
I can't believe you think that the Pandavas - or Bhishma - are terribly flawed persons.