While I get what you're saying, I think it's worth pointing out that Beserk and the Star Wars prequels deal with very different character types, and very different falls.
The implication I got from the end of Beserk was that Griffith was always a bit of a sociopath. Not just sociopathic tendencies, but a full on sociopath. Throughout the series, we see that he's always valued the pursuit of his own dream over anything else. Whether he is fully aware of the Behelit and the whole 'demonic transformation' thing or not, it seems like he always knew that he was going to have to climb a mountain of corpses to get where he wants to go, and he just doesn't care. He doesn't so much 'fall' as willingly dives in. Now, you may disagree here, but my interpretation is that the only thing that gave him a moment's pause was the appearance of Guts, and what appears to be a very homoerotic attraction to him by Griffith. I know a lot of fans deny that, but for me the subtext in the anime is too strong to ignore. Griffith is willing to sacrifice everything right from the outset in order to achieve his dream, but the appearance of Guts gives him a brief period where he actually cares for someone other than himself. As soon as Guts fucks off, he reverts right back to being a selfish ****, going so far as to quasi-sorta-rape the Princess in order to make himself feel good. Cut to a year later, and he willingly murders the very people who rescued him in order to finally achieve his dream, and rapes Casca in order to get back at Guts for symbolically 'dumping' him.
I see the Eclipse not as Griffith falling, but as him finally manifesting as the **** he always was. Or at least, had been since a little kid. He was never a 'good' person, and the reason Beserk works so well is because in looking back, you realise that Griffith was always a heartless bastard.
Anakin is different, in that the story has to revolve around him at one point being a genuinely decent person. Griffith, as far as I'm aware, hasn't shown any sort of repentance or regret over his frankly awful actions. Whereas the Star Wars saga relies on Anakin/Vader eventually coming to regret his decisions, and briefly reverting back to a decent character before he dies. If he had always been a sociopath like Griffith, there would be nothing for him to revert back to. There'd be no remorse, as he'd feel genuinely empowered in his position as an evil Sith Lord. Whereas in the prequels, he may be whiny, bratty and self-centred, but you can at least get the impression (even if the execution is lacking) that at this core, he's supposed to be a decent person. Someone brash, egotistical and conceited, sure, but someone who genuinely wanted to do what was right.
