Actually, not true. Just because they were imbued with the powers of the event, that does not give any indication of their powers before the event. If you were to imbue a Vaporeon with Water, Fire, and Lightning, it might very well become a much bulked up Pokemon, but its affinity for Water causes it to absorb the water infusion better than the others, keeping it a pure Water type.
In fact, that could make more sense than them being Normal typed, since if you infused a Normal with water from the storm, wouldn't you get a Water-Normal type Pokemon? But the beasts aren't dual-typed.
There is no indication at all about what they were before the tower burned down. Nintendo has told us nothing. What you presented as "facts" were personal interpretations, nothing more.
As it happens, I don't really disagree with your idea. Eevee is the most variable Pokemon there is, and has ties to the city through the Kimono sisters. But please don't pass speculation off as fact.