I don't know how that fucks up his character in the OT? How does it fuck up his character from the OT? The fact that he was more willing to kill people directly?the Vader scene at the end. Although, while the Vader scene was cool, it fucks up what his character is in the original movies and even kinda what the force is there.
Though the thing with the Force is just what you're always going to get whenever you set a Star Wars story in the past. You're come up against the nerd question of "Why didn't they do that shit in Luke's day? Why did Old Ben fight like an old guy who didn't really know his way around a sword?" It's one reason I wish they would stop plundering the pre-Yavin eras for material, and just do new shit. Otherwise, they feel obligated to always make references to the OT, have things that connect back to it, no matter how heavy handed it is to shoehorn it in. And for R1, an entire film about a single plot point that the fans blew WAY out of proportion, that they felt they needed an entire damn film just to shut them up.