TEATD preserves his moment of sacrifice, gives him a very epic final death. Not only that, he's pivotal in that he convinces the Emperor not to become a Chaos god to defeat Horus and gives him the only weapon that can kill Horus at this point,
Hmm ... Emperor perceived as an enlightened superhuman who effortlessly defeated the lies/temptations of Chaos, and now suffers in service to all mankind on the Golden Throne as a Bodhisattva-esque figure?
As to my own opinion on FSM, I would have no problem if they had been possible from the start, but as it is SM have been all-male for more than 30 years and I see no compelling reason for making such a change.