I don't know where this "Mega Ray is unfair" argument come from. As a Mega Ray user, I feel like it's kind of overrated. Just because it's better than everything else in ubers, doesn't mean it's broken in here.
In fact, I'd say Mega Salamence is a better god than Mega Ray because it's bulkier (especially with Intimidate), get Roost and Refresh to heal itself from damages and status. Because of this, it doesn't really need Healing Wish Latias support, which is very important because you can fill that slot with a good poke that covers more threats.
As for sweeping, Xerneas is harder to stop than Mega Ray because of how easy it is to 6-0 things with Geomancy and team support.
Mega Ray IS good though, just not as "unfair" as people making out to be.
xern can be checked, incapable of going mixed, unable to hold an item, and lacks a "reliable" typing. lets not forget, mega rayquaza has 115 speed, 180 offenses, 120 stab with negligable recoil, capability of holding an item, reliable and strong priority, AND an ability to help deal with specific pokemon who would otherwise revenge kill. for example of its attacking power:
+2 252 Atk Life Orb Mega Rayquaza Dragon Ascent vs. 252 HP / 252+ Def Mew: 469-554 (116 - 137.1%) -- guaranteed OHKO
+2 252+ SpA Fairy Aura Xerneas Moonblast vs. 252 HP / 252+ SpD Mew: 328-387 (81.1 - 95.7%) -- guaranteed 2HKO after Leftovers recovery(take note the modest)
115 is a speed tier that both ubers AND OU covet to outspeed, and on top of that, ray gets 2x priority, and neutrality to ALL priority but ice shard, which is only 2x effective.
what makes ray scary is that it's stats are complimented with the fact that its speed tier lets it outspeed EVERY relivant mon, and the ones that do outspeed die to espeed. and ray also has the bulk+typing(delta stream) to set up on almost every pokemon in the tier.
the main difference between mence and ray, is ray gets swords dance, and the ability to have a "fools aerialate" with life orb. ray is still stronger by a massive 40 base points and has priority to back it up alongside running DD if it was crazy enough to do so( with more resists and lacking a 4x weakness to ice because of delta stream allowing it more setup opportunities to top it off) not much of a "better" case (as mence gets 95/130 bulk with intimidate!) buuut, id still take 180 attack over 145 anyday, especially when that "30% boost" is on ALL of your moves, rather then just your flying type moves securing more ko's.
and also, if ray gets a swords dance, your team probably loses. if you predict the SD and phase it away...it just comes back in and swords dances again. xern cannot do that. that's another difference between xern and ray.
and lastly, lets not forget both dragon and flying are FILLED with amazing revenge killers, sweepers, and wallbreakers as is.
i think its unfairness is pretty justified. as both offense and stall would be hard pressed to fight this thing, and
unlike xern, its not a case of "oh man i have to defeat that aegis and win" its literally "oh, my opponent locked himself into CC, time to come in and get a kill" xern is good because if given the opportunity, it can completely wipe a team clean. ray can do that without having to prepare so cautiously for such a chance, while still lacking reliable revenge killers like scizor and aegislash to combat it. seriously, it uses PRIMAL GROUDON as setup fodder. and ohkos max def at +2!
+2 252 Atk Life Orb Mega Rayquaza Earthquake vs. 248 HP / 248+ Def Primal Groudon: 374-442 (92.8 - 109.6%) -- 56.3% chance to OHKO
