Here is a more balanced approach to Celebi + Wobbuffet with Jirachi and Celebi being the main defensive core while Wobbuffet is a catch-all check. Celebi is the Physical Defensive Tank because it has the uncanny ability to switch into pretty much any ground attack that Jirachi/Victini fear, including the likes of Excadrill, which could break the standard Latios with Mold Breaker. It also serves as a standard utility Pokemon with Twave, Stealth Rock, and Recover, and with Natural Cure, it can also switch into any status that may threaten the rest of the team. Jirachi was the natural pick for a special defense tank, pairing very nicely with Celebi, resisting Ice and Flying attacks that Celebi doesn't like while being neutral to Bug ones and flat out immune to poison ones. However, this set is a personal favorite of mine because of how annoying it can truly be. Rather than Para-Flinch, with Toxic, the opponent is losing health each turn. And with a Flinch, they are rendered immobile for that turn, letting the Toxic chip do its work with Wish as Jirachi's form of recovery. Then Protect brings this entire set together, combo-ing nicely with Toxic, and Wish, allowing Jirachi to Toxic stall, Get the Wish heal, or even just recover with leftovers. Rounding out the Defensive core is Wobbuffet who just catches pretty much everything that isn't a Special Dark pokemon or a Physical Ghost. The Colbur Berry also allows Wobbuffet to always check Mega Sharpedo as well, one of the biggest threats to Psychic. Now the offensive core is more specifically designed with each Pokemon selected for its abilities in the 3 weakness matchups Psychic faces. Mega Gallade with Justified is very good vs Dark with Close Combat wiping pretty much everything out at +2 with the exceptions of Mandibuzz which tanks CC and Ice Punch at +2 and ohko's with Foul Play, Mega Sableye which is immune to CC but has to be weary of a +2 Ice Punch, and Mega Sharpedo which outspeeds and does a lot of damage with Crunch. Gallade also has the added benefit of easing the Poison and Steel match ups as CC handles Muk very nicely and CC hits most things on Steel SE. Victini is the pokemon of choice for easing the Bug match up, while also aiding in the Dark MU with Scarf Uturn, and the Steel Match up with Scarf Fire moves when Heatran is gone. And then Meloetta is a monster in the ghost match up. However, since I am running Mega Gallade as well, I opted for Dazzling Gleam over Focus Blast to hit Mandibuzz and Mega Sableye with SE hits.
Note: I was going to edit my team to fit a Defogger in there, but Latios is unnecessary with Celebi taking the ground hits and Meloetta being the special attacker of the team with Scarf Victini as the speed control, and Jirachi complements Celebi better as a Special Defense tank than Mew does, so I opted out of a Defogger as the only thing majorly chipped by Stealth Rocks is Victini. However, Webs will be a hindrance, especially if a scarf Heracross is running around, but Jirachi lives a +1 Megahorn from Heracross and can work on Toxic Stalling it. Other than Heracross though, webs can be worked around as well. And simply don't let 3 layers of Spikes go up.