Rhythms,
xJownage and
Lcass4919 - Let me try to respond to all of you at once :) And sorry Rhythms, I mean I drew the conclusion that I should speak up about this, not let it sit in the back.
It should come down to consistency, because there's a thin line we go down when it comes to subjectivity and objectivity. So, we agree that Smeargle isn't broken with Geomancy and Xerneas is broken with Geomancy, and we ban Geomancy, and lets be fair now, you would've banned Geomancy even if Smeargle didn't learn it - because it literally doesn't matter if it does or doesn't because it's useless. Then we would be going down the road of subjectivity, and that's a road equal to the objectified one. Where you, the leaders, personally figure out what breaks a mon then removes said aspect.
Right now, banning Xerneas is perfect. It solves the problem, and leaves you with one set to play with (Scarf, everything else outclassed by Arceus-Fairy). But in the long term, it's horrible. What if there's new pokemon introduced in SM that we ban to, but you can just remove one or two aspects of them and now they're balanced. Or Mega-Rayquaza, if we just... Remove the item slot. It would take up such a large amount of time.
I realise I'm not going to convince you all, it's impossible to address all your concerns at one time, especially when arguing with three people, but the broader part of my argument is:
It's to subjective, Xerneas either is or isn't broken, if you remove on aspect of a pokemon then you're starting on a slippery slope until you're banning hundreds of things to make sure everything is playable - this will take up to much time to feasible