Problem with comparing P2 to P-Z is that..........you sorta cant. P-Z is a sweeper with ridiculous base strength, while P2 has a respectable attack prowress and phenominal bulk. One does not out class the other, but here in OU P2 is more viable only because it doesn't face a lot of competition in mixed walling that can comfortably say they are on his level. If we were, we would demonstrate how the OU metagame prefers one over the other and that as a team choice P-Z is inferior option, but if people like using P-Z, then let em use him and congratz if they get him to work. Be more happy to give the option than deny it.About Porygon-Z, wouldn't it be better to show why it is inferior to Porygon2, rather than shoving it down the player's throat by not allowing it period? The same could be said of Gallade, Glalie, most of the Eevolutions, and even Phione; would Rotom-W be independent of Rotom? Aside from that, if Mantine and Escavalier are included as being OU viable, then Shelmet and Remoraid will need to be included as well, unless a perfect Escavalier was given to the player and Mantyke was wholly taken out.
It seems like it would be a good idea to have a few unviable pokemon out there, if only to show what works and what doesn't, and even to force some creativity; one of the best battlers I know runs an OU team half comprised of RU mons, so it isn't too far out there. I'm not saying that every pokemon should be included, but at the very least, those who would normally be obtainable simply because they're related to someone who's actually on the list should be.
We will show what works and what doesn't, but as expressed by most, lots of good mons work in OU that are actually UU or lower, and if they use em great, let em. One excellent example is Hippowdon. xD