Why is it that whenever someone posts for Colo to go up, I feel I need to post for it to go down. Its a good Pokemon, sure, but it is nowhere near as good as the other S guys. It can do a lot, but so many good guys can handle it easily. Tomo and Mega Altaria in particular can just pick it apart. Other good guys such as Clefable, Mega Sizor, Sylveon, Keldeo, Mega Lopunny and Mega Venusaur can all check or counter it. Furthermore, by far its most popular set is Assault Vest. Even with some investment, without a vest, it cannot stop special attackers. This is a massive detrament for it, as it means that so often it is a Dark resist that cannot reliably absorb Knock Off.
Compared to the other S rank Pokemon, Colossoil is nowhere even near as reliably useful, and I find it hard to justify it for A+, much less S. (So yeah, that does mean I am totally saying it should be A [or even A-])
On a different note, can we like, not, have S-. S really should be those mons that are just a cut above the rest. If it is not really as good as other S rank mons, then that should mean it is A+, not S-. No other tier has S divided up in thier rankings for this very reason (well, except ubers, but that is with an S+ for P-Groudon, and if you know anything about ubers, you know that is an exception that nothing here even comes close to). There are so many ranks as it is that this just feels so unnecessary.