Kommo-O is interesting because it only rose to OU recently. Most sets suggest that Kommo-o Stay away from Fairies and either have Dragon Tail+Stealth Rock (defensive role), Stealth Rock+Clangerous Soulblaze (split role), or Belly Drum+Substitute (offensive). Iron Defense and Protect seem like an odd gimmick to me, especially when one Dazzling Gleam will OHKO Kommo-O :P
I don't think Mismagius will do well at all in OU because the Def and HP Ev's aren't going to do much when Mimikyu, Bisharp, Landorus-T, Tapu Koko, Weavile, Flying/Levitate Pokémon, and the moves Volt Switch/U-Turn exist and are common in OU. :P
A Suicide Lead Shuckle is the only Viable Shuckle in OU, mostly due to Chansey, Toxapex, and Taunt's Presence. :P
Upon reading all content on this page, I assume you are playing on a DS and not Pokémon Showdown!, and therefore your choices may be limited. If this is correct, while Legendary Pokémon aren't necessary, you should be able to get Tapu Koko, Tapu Lele, Tapu Fini, Tapu Bulu, and all the ultra beasts in OU easily. If you have Ultra Sun/Moon, Tornadus-T, Mega Lati@s, Thundurus, Zapdos, Heatran, and Blacephalon should also be easy to get, and Landorus-T and Kyurem-Black can be obtained if you have the two other legendaries in their trio. Granted, you still miss out on Magearna, Victini, Diancie-Mega, Hoopa Unbound, Keldeo, and Mew. :P
If you aren't on the DS and use PS!, I recommend you use whatever benefits your team, albeit legendary or not. Not doing so would be a bad team-building practice, as you limit yourself unusually to use all of the Pokémon in one tier. They are all in that tier because they all compete on a relatively level playing field, meaning that that Legendary is just as good as the other Pokémon in the tier, meaning it isn't OP to use it, but not considering it limits your team-building flexibility and may cause sub-optimal synergy. :P
