To build on to Zekrom's rate:
Night Slash > Leaf Blade on Gallade, simply because a 2x super effective Leaf Blade does the same amount of damage as a STAB neutral Close Combat:
-2x supereffective Leaf Blade: 90 x 2 = 180
-STAB neutral Close Combat: 120 x 1.5 = 180
Unless you're deathly afraid of Quagsire, Gastrodon or Swampert (the last one for some weird reason, considering it's not commonly used anymore), Night Slash provides better coverage with Fighting/Psychic.
As mentioned before, Mega Alakazam is too frail to set up Calm Mind. Better options in the last slot are Hidden Power Ice/Fire, assuming Alakazam has either Hidden Power type, (in order to deal with Dragonite, Landorus and Gliscor, and Ferrothorn and Scizor, respectively), Substitute (to have a buffer against status or other moves on a predicted switch) or Protect (to Mega Evolve safely, given Alakazam's general frailty). Tl;dr:
-Psychic
-Shadow Ball
-Focus Blast
-Hidden Power (Ice/Fire)/Protect/Substitute
Nature: Modest
EVs: 4 HP/252 SAtk/252 Spe
Item: Alakazite
Ability: Magic Guard
If you can use Poke Transfer, Mega Gardevoir needs Hyper Voice over Moonblast. Pixilate doesn't affect moves that are already Fairy type, and it only benefits Normal moves, so if Mega Gardevoir doesn't have Hyper Voice, there's absolutely no reason to use the Mega Evolution at all. And Mega Gardevoir's 100 Speed is rather good; why are you wasting that away by investing in bulk? It's still physically frail with investment. Shadow Ball doesn't see much use at all, unless it's for Aegislash. However, given Aegislash's popularity in Battle Spot, you
could use it. Trace is also the preferred ability pre-Mega Evolution so that Gardevoir has utility in copying defensive abilities upon switching in, like Intimidate or Flash Fire. Much better set down here:
-Psyshock
-Hyper Voice
-Focus Blast/Shadow Ball
-Taunt/Will-o-Wisp/Calm Mind
Nature: Timid/Modest
EVs: 24 Def/232 SAtk/252 Spe
Item: Gardevoirite
Ability: Trace
Also, here's a better set for Wobbuffet; it's too slow for Destiny Bond; Safeguard is the better option to protect the team from status:
-Counter
-Mirror Coat
-Encore
-Safeguard
Nature: Calm/Bold
EVs: 28 HP/252 Def/228 SDef
Item: Sitrus Berry/Leftovers
Ability: Shadow Tag
Although it seems like a good idea to put Mega Stones on two Pokemon for "versatility," it's really never a good idea. Magic Guard lets Alakazam abuse Life Orb without taking the recoil damage. Also, Alakazam doesn't do much with Energy Ball. Focus Blast is the better option.
Wobbuffet isn't really a big threat anymore, and there are plenty of much better options, such as Reuniclus, who can also run a very powerful Life Orb set; Slowbro, who can be used as a physical wall; or Starmie, who can be used as a fantastic sweeper.
You're underestimating Mega Alakzam's effectiveness. It has utility in using opposing abilities with Trace, i.e. copying Kingdra's Swift Swim, then KOing it in return, copying Dragonite's Multiscale to compensate for frailty. While the loss in Magic Guard sucks for Mega Alakazam, Modest Mega Alakazam hits harder than Timid regular Alakazam. 150 Speed outspeeds base 130 Speed Pokemon, even with a neutral nature. In all cases, Alakazam's best time to be brought in is after a teammate is KOed.
Wobbuffet still has some utility in eliminating/making counters setup bait with Shadow Tag. However, here are Slowbro and Starmie sets should the need arise:
Slowbro:
-Scald
-Psyshock/Ice Beam/Fire Blast
-Thunder Wave/Toxic
-Slack Off
Nature: Bold
EVs: 252 HP/232 Def/24 SDef
Item: Leftovers/Rocky Helmet
Ability: Regnerator
Starmie:
-Hydro Pump
-Ice Beam
-Psyshock/Thunderbolt
-Rapid Spin
Nature: Timid
EVs: 252 SAtk/4 SDef/252 Spe
Item: Life Orb/Leftovers
Ability: Natural Cure