I think Lugia should be water type... because it is considered guardian of the sea...
And then you'd have a Legendary that would wet itself at the sight of one good STAB Thunderbolt and then the masses would whine it was too weak.
For people who think this is a worthwhile complaint, ask yourself what alternatives you yourselves can come up with. If you have a Legendary Pokémon whose design doesn't invoke any particular type and you need it to have access to a strong moveset with relatively few type-based weaknesses, what better type is there than the Psychic-type? Did you want the pixies to be Water-types, maybe?