I'd like to petition this out in asking if we could instead dump the idea of having any legendaries and pseudos altogether. Instead, the idea of mythical common Pokemon (i.e - Arcanine, Volcarona, Ninetales, Lucario, etc.) floats more comfortably to me. I already dumped the notion of using a pseudo, and Strat kinda helped me realize there were better options. To me, I understand that pseudos and legends already just have that placebo effect of just POSSIBLY being included into our party. Granted, Strat could nerf them, but at the end of the day, I think it defeats the purpose of having such a Pokemon. This is in Stratos' own words "where the anime messed up" and not the games. BSTs should be irrelevant. (I mean when a Pikachu defeats a Dragonite, in the games it is irrelevant). Of course he's giving us options later on, but I believe most people might vouch for one. I certainly will if given the chance.
My point: I feel like legends and pseudos aren't something to just toy with, where I think it'll make smallish Mary Sues out of us. And the concerning the "character fitting" legends: there are other non-legendary options. Someone said Darkrai would fit their character perfectly. There's other viable options for what Darkrai represents, in forms such as Zoroark and Gengar.
I'd just think it'd be easier without legends or pseudos in the story, and leave it to NPCs.