My thoughts on these, Mega Pinsir Mega Altaria, Mega Charizard X, Zapdos, Mega Sableye and Landorus-I.
Mega Pinsir creates the situation in which whoever sets up Swords Dance wins in Bug verse Bug game, although, I believe this is mitigated by its lesser bulk and weakness to Stealth Rock which makes it much more manageable. It really beats only two types because Fighting can easily deal with it, with the likes of Stone Edge on Terrakion. This being said Bug can beat it with Armaldo or Forretress, as they can take one of its moves and Rock Blast or Thunder Wave it respectively. Grass can give it some trouble with Sash Breloom. Moreover, this is the only thing that beats it and Grass also loses to Volcarona, so in general Grass loses this match up. No Ban. Edit: The reason why Talonflame was more deserving of a ban was that Talonflame has more innate power in its priority. Almost doubly so.
Mega Altaria is two monsters, and as such it should be address as Altaria (Flying), and Altaria (Dragon).
Mega Altaria Flying does not see usage and thus should have less reason to be suspected, and if OU banned Altarianite, it would most likely trickle down to Monotype like Baton Pass did. Otherwise, I see absolutely no reason in banning a Pokemon that sees such little usage, like really it is like banning an Underused Pokemon to Ubers, I cannot recall a time where this has happened unless this Pokemon got a huge boost. Um, guess, no ban. If Charizardite X were to be banned I would then agree on this being banned, after seeing how the metagame develops.
Mega Altaria on Dragon is very powerful and is used very often, in comparison, but really does this auto-win verse some types, such as Dark, Fighting, Electric and Dragon itself. For all of you who say it auto-wins verse Water, I personally have never had this happen to me, although I use Water more often than not. So, I count four types it can auto-win against and I feel this is more than enough to be banished to the Uber realm. So, Altarianite on Dragon only should be banned.
Mega Charizard X is extremely potent, versatile threat with solid recovery, and Will-O-Wisp. Mega Charizard gives Flying a way to deal with BoltBeam as well as completely destroy Psychic, Dragon, Ice, Electric, and Grass without much team support barring Heal Bell Togekiss. It also completes defensive cores due to its resistance to Electric and neutrality to Ice. Thus, allowing it to form both Defensive and Offensive cores with ease. It is just literally the perfect Mega for Flying, and the fact it auto-wins verse two types Flying is weak against, makes it more than ban worthy, and should have been banned a long time ago. So needless to say, ban!
Zapdos, ugh, anyone remember the defensive Flying core that cause so many problems, well, even if Flying has both Mega Charizard X and Mega Altaria banned I would never want this defensive core back, it just fucked so many types, and made anyone say that the best type was Flying. Like really, I had difficulty with Flying almost every single time although it has a neutral match up verse Water. Skarmdos is just broken. Please keep this thing banned.
Mega Sableye, um, people have problems with this thing, like I get the fact that it is good, but all in all, this is easy to beat if you play right. You need to avoid the turn it Mega Evolves because it has Prankster and then just beat it with any Attacker that is immune to the burn or outspeeds and can OHKO or 2HKO while being burnt. I just use SubCM Keldeo set up along side it and then Scald it to death, as Burn neuters it so much I even healed my Lanturn of this thing because Thunder Waving it gave me my health back. Just learn how to play around Magic Bounce...
Landorus-I, I take this is just because it was banned from OU, and I get that. Therian is preferred on Flying and Ground just received a nerf calm your nips, and let the meta develop.