While I completely agree that Ho-Oh is a large and shaping part of our metagame, the fact is that by the very definition of S-Rank, its ineligible.
Now, that being said, I do believe it could be time the whole 'definitions' of each tier was restructured a bit to better accomodate the pace of the metagame and the direction in which its headed - e.g it's extremely clear that PDon is the biggest factor on the metagame as of now, and is as such at the top of the viability rankings - however, one must admit that it requires more team support than, say, Gengar-Mega, who remains ranked below it.
tl;dr - While I believe Ho-Oh deserves a top tier ranking, the parameters of said top tier are too binding, and could use a bit of restructuring.
They barely require support, if any, from the team
Now, that being said, I do believe it could be time the whole 'definitions' of each tier was restructured a bit to better accomodate the pace of the metagame and the direction in which its headed - e.g it's extremely clear that PDon is the biggest factor on the metagame as of now, and is as such at the top of the viability rankings - however, one must admit that it requires more team support than, say, Gengar-Mega, who remains ranked below it.
tl;dr - While I believe Ho-Oh deserves a top tier ranking, the parameters of said top tier are too binding, and could use a bit of restructuring.