That's a very good point regarding Mr Garak (shockingly the G'kar comparison had not occurred to me, and me a B5 fan
) in many ways he is not the typical fictional hero because he doesn't die in a blaze of Glory and he has committed terrible acts in the cause of his peoples eventual freedom. (attempted genocide of the Dominion's Founders, the murder of a Romulan Senator and a con artist to name two key insistence's).
However it is a basic truth that Garak did these things not for his own aggrandisement but for the people of Cardassia and the AQ. It seems to me that Garak is indeed a realistic hero and a great character.
I would argue that Damar had to die at the end of the DW because it that is how it had to be. Corat Damar was still a product of the old 'poisonous ideology' who had murdered an innocent young woman and been a part of a war that had claimed the lives of billions. Damar's rebels helped to save the AQ and perhaps Cardassia's soul but the man himself was still too much of a Central Command figure to really play a part in the new Cardassia.
Instead Damar became a martyr to the cause of Cardassian freedom.
(still, it would have been fulfilling to see Damar have to wrestle with his guilt regarding Ziyal and his role as the 'leader' of Cardassia...)