Although this may "defirm" Mewtwo for some, I'm gonna stay in denial for a while longer.
This could still be part of a "grand troll", especially since that other guy got a WFT trophy without beating classic with her. It could help keep DLC under wraps by having us assume that every trophy character is automatically defirmed, when really, some of them may just get in.
Again, it's not over until it's actually over. And trust me, it's not over, yet. We're pushed to a pessimistic corner and odds are seeming incredulously low, but there's still somewhat of a possibility, however slight.
That's the thing. Sakurai is an actual troll. A lot of what we're going off of isn't truly confirmed yet, but is what's most likely based on what we have to observe at the moment, meaning we can take a lot of things a lot of ways until we truly get some undeniable confirmation, which is why some people are giving up on Mewtwo here, and others are still holding out.
I'd say it's best to try to hold out, and not finalize one's opinion until we get some true confirmation from Sakurai. Trophies make things bleaker, but that doesn't erase the possibility of the character's inclusion. The ever-so-slight possibility of this being able to be a huge red herring to what's actually happening is enough to maintain some hope for me. What we don't know is more important at this point.