>>22359555If you're saying that from a lore standpoint, it's because Arceus isn't necessarily the strongest even according to lore.
It being the creator of the universe doesn't grant it huge strength. Those things usually go together, but they're not mutually exclusive. Typically people associate Arceus with the Christian view of a God which is both the creator and all-powerful, but it's not even based off of that. That's just a western-centric view and assumption.
Nowhere has it been stated that Arceus is the strongest pokemon, not even in the iffy arguably false lore of the game. The only pokemon that has a title like that is Mewtwo, and even the lore is inconclusive about that.
The only thing you can deduce is from the pokemon's actual stats-- mathemetical representations of the pokemon's actual ability.
In that sense, M-Rayquaza is undeniably the strongest as of now.