The "shot into the timestream" aspect was revealed in Final Crisis, way before Cap Reborn came out. And while Marvel did the "former sidekick takes up dead hero's mantle" thing first (in this case at least), that grew out of the "long dead sidekick comes back as villain" plot they "lifted" from DC (Red Hood/Winter Soldier).
I think this is an X-Men/Doom Patrol, Swamp Thing/Man-Thing type scenario. It doesn't matter who's copying who, what matters is who's doing it best.
