You could bring up the whateveritscalled tower housing Groudon/Kyogre in HGSS, but that was more a way to give us accessability to those legendaries than anything else.
I chose Hoenn and Sinnoh specifically in my post, because both of them have their own seperate creation myth.
Both have a set of legendaries representing aspects of the real world, and a story of them creating the region they reside in.
This is clearly contradictory if you took the MYTH (=made up story) serious.
Regardless there is still no argument for legendaries being more than powerful ancient rare pokemon.
It is those qualities that inspired the myths and legends.
There are arguments against it though. Like catching them in pokeballs and using them in battles like any other pokemon.
"Capturing it or defeating it will make this world disappear!"
*player catches Giratina*
nothing happens... Cyrus is surprised.
Conclusion: Giratina is simply the only thing that lives in the Distortion world. It didn't create it and it doesn't control it.
I see what you're trying to say, but we won't really know until a remake of Ruby and Sapphire comes out. However i still strongly believe that Arceus is truly the creator (However way it did) since it is the strongest Pokemon i have seen both in the anime and the games.
Also if the world crumbles when Giratina is caught because of unbalance in Platinum, the game would end.
Plus were Groudon and Kyogre the ones who created Hoenn? Because Groudon raised continents. While Kyogre raised oceans (which will obviously affect the whole world. Also when Kyogre is awakened in Sapphire, Steven says that the downpour will flood the entire World. Not to mention Rayquaza controls weather, not the weather in Hoenn.