Ok ok, I make to many of these, but this one will be short and sweet and totally goes against another theory I have: 'were Cyrus and Lysandre working together?' I got some of the content off of Lysandre's description on Bulbapedia.
Ok, so Lysandre and Cyrus have the same eye color: Blue. They look similar. Their goal is also similar; both involve trying to wipe out everyone for some purpose and using Legendary Pokémon to achieve it. They also use the same Pokémon: Murkrow/Honchkrow and a Gyarados. Lysandre's second in command Xerosic, uses a Crobat, another of Cyrus' Pokémon. Mable, one of Lysandre's scientists, uses a Houndoom and a Weavile, also Pokémon Cyrus had.
What I'm saying is that maybe Cyrus had fled to Kalos in Pokémon Diamond/Pearl and in Platinum he escaped the distortion world and landed in Kalos. And having failed, made another attempt to use legendary Pokémon to destroy the world from all the filth that makes it that way.
See? Short and to the point. So what do you guys think, criticize all you want. Or you could go to my other theory and see which one you agree with better. Either way, bring me the pain!