I feel like the only real Fairy Latios should worry about it MegaGardevoir since it is immune to one, resistant to the STAB and can OKHO with Hypervoice.
252 SpA Pixilate Gardevoir Hyper Voice vs. 4 HP / 0 SpD Latios: 422-498 (139.7 - 164.9%) -- guaranteed OHKO
Granted MegaGoddess will not want to actually switch INTO Latios because:
252 SpA Choice Specs Latios Shadow Ball vs. 4 HP / 0 SpD Gardevoir: 204-240 (73.3 - 86.3%) -- guaranteed 2HKO
252 SpA Choice Specs Latios Psyshock vs. 4 HP / 0 Def Gardevoir: 139-164 (50 - 58.9%) -- guaranteed 2HKO
252 SpA Life Orb Latios Shadow Ball vs. 4 HP / 0 SpD Gardevoir: 177-208 (63.6 - 74.8%) -- guaranteed 2HKO
252 SpA Life Orb Latios Psyshock vs. 4 HP / 0 Def Gardevoir: 121-143 (43.5 - 51.4%) -- 7.4% chance to 2HKO
252 SpA Expert Belt Latios Shadow Ball vs. 4 HP / 0 SpD Gardevoir: 163-192 (58.6 - 69%) -- guaranteed 2HKO
252 SpA Latios Psyshock vs. 4 HP / 0 Def Gardevoir: 93-110 (33.4 - 39.5%) -- guaranteed 3HKO
***252+ SpA Choice Specs Latios Shadow Ball vs. 4 HP / 0 SpD Gardevoir: 222-262 (79.8 - 94.2%) -- 43.8% chance to OHKO after Stealth Rock***
So really in terms of Fairy-types Latios doesnt really have much at all to worry about. I would never say switch-in or go 1v1 against a MegaGardevoir but if it catches it on the switch it should be ok
252 SpA Pixilate Gardevoir Hyper Voice vs. 4 HP / 0 SpD Latios: 422-498 (139.7 - 164.9%) -- guaranteed OHKO
Granted MegaGoddess will not want to actually switch INTO Latios because:
252 SpA Choice Specs Latios Shadow Ball vs. 4 HP / 0 SpD Gardevoir: 204-240 (73.3 - 86.3%) -- guaranteed 2HKO
252 SpA Choice Specs Latios Psyshock vs. 4 HP / 0 Def Gardevoir: 139-164 (50 - 58.9%) -- guaranteed 2HKO
252 SpA Life Orb Latios Shadow Ball vs. 4 HP / 0 SpD Gardevoir: 177-208 (63.6 - 74.8%) -- guaranteed 2HKO
252 SpA Life Orb Latios Psyshock vs. 4 HP / 0 Def Gardevoir: 121-143 (43.5 - 51.4%) -- 7.4% chance to 2HKO
252 SpA Expert Belt Latios Shadow Ball vs. 4 HP / 0 SpD Gardevoir: 163-192 (58.6 - 69%) -- guaranteed 2HKO
252 SpA Latios Psyshock vs. 4 HP / 0 Def Gardevoir: 93-110 (33.4 - 39.5%) -- guaranteed 3HKO
***252+ SpA Choice Specs Latios Shadow Ball vs. 4 HP / 0 SpD Gardevoir: 222-262 (79.8 - 94.2%) -- 43.8% chance to OHKO after Stealth Rock***
So really in terms of Fairy-types Latios doesnt really have much at all to worry about. I would never say switch-in or go 1v1 against a MegaGardevoir but if it catches it on the switch it should be ok