Flaws don't make a good character. The over coming of flaws make a person worth remembering. Its the notion of why Batman is better than Superman. If your perfect then doing great things is to be expected, because its easy for them. But if your mortal and suffering and still manage to do right and great things its speaks more about who you are. Kirk is a bit of a horn dog, but he manages to rise about his biological tendencies to be a great captain/man, a symbol for other starfleet officers to inspire too. He shows that character can overcome our human weakness.