Erm. I personally run the special hyper voice/tail wind set on my Mega Altaria. I looked at using a physical set. But was met with comments such as "Why bother, physical Mega Mence is better + faster"
Sure, Mega Altaria gets the fairy typing. I still wouldn't bet on Altaria in a showdown 1V1 with Mega Rayquaza
Mega Mence is surely faster than M-Ray but in a 1v1 situation where both Pokémon are healthy, Lv 100 (though usually in a VGC situation Pokémon are set to Lv 50) and do their max damage (no critical hits) and without stat boosts, Mega Mence eventually loses out if it doesn't have Return and just spams Double-Edge.
So:
252 Atk Aerilate Mega Salamence Double-Edge vs. 0 HP / 4 Def Mega Rayquaza: 276-325 (78.6 - 92.5%) -- guaranteed 2HKO
Because of recoil damage, Mega Mence could lose up to 108 HP. Mence shall have 223 HP remaining (no EVs, 31 IVs in HP).
And there's Rayquaza's Dragon Ascent:
252 Atk Life Orb Mega Rayquaza Dragon Ascent vs. 0 HP / 4 Def Mega Salamence: 259-305 (78.2 - 92.1%) -- guaranteed 2HKO
It does up to 305 HP damage, which is enough to KO Mega Salamence (even if both Pokémon do their min damage).
But if Mega Salamence used Return instead:
252 Atk Aerilate Mega Salamence Return vs. 0 HP / 4 Def Mega Rayquaza: 235-277 (66.9 - 78.9%) -- guaranteed 2HKO
252 Atk Life Orb Mega Rayquaza Dragon Ascent vs. 0 HP / 4 Def Mega Salamence: 259-305 (78.2 - 92.1%) -- guaranteed 2HKO
And:
252 Atk Aerilate Mega Salamence Return vs. 0 HP / 4 Def Mega Rayquaza: 235-277 (66.9 - 78.9%) -- guaranteed 2HKO
This time Mega Salamence wins out.
Mega Mence doesn't win out all the time but it just depends on what moves you put on it and the current battle situation.
If it used Outrage, it would surely be a OHKO because Strong Winds doesn't affect Mega Rayquaza's weakness to Dragon.