Cubes was eventually going to find a way to screw the Dokes over. Homura simply took the burden on herself, sacrificing her own happiness so that Madoka and the other megucas could live happy lives.
>Cubes was eventually going to find a way to screw the Dokes over
Nope, Homura was the Incubators only chance.
Everyone who was able to access her barrier did it only because they were invited from within by the Clara Dolls. Homura was the only girl who still had memories from the past world and had a connection with the forgotten Madoka, thus the only one who could invite her (and LoC) into her world.
Saying that they eventually would be able to do it when the only method that worked is so specific is just speculation.