You're right, I'm tired as shit and didn't really read the whole question, just assumed the Q was what role does it serve mainly.
To me it just seems outclassed on every front. As a Z-bulky Rocker Landorus outclasses, we have a plethora offensive Psychic-types, for main example, Tapu Lele. Stored Power sweeper we have Mega-Latias. It is just simply outclassed in terms of typing, stats and ability for every role it tries to fill. Its speed sucks, its not really that bulky and has an defensive typing that offers very little in the way of useful resistances, especially compared to competition defensively (just use mew? if Psychic-type for some reason is attractive), and its SpAtk is nothing to rave about either especially when we have Hoopa-U or even Mega-Alakazam (Hoopa being very comparable offensively and a lot better).