Groudon/Xerneas lead basically wrecks that though, with Earth Power/Precipice Blades KOing Gengar and Arcanine.
-1 252 Atk Primal Groudon Precipice Blades vs. 0 HP / 4 Def Arcanine: 152-182 (92.1 - 110.3%) -- 56.3% chance to OHKO
-1 252+ Atk Primal Groudon Precipice Blades vs. 0 HP / 4 Def Arcanine: 168-200 (101.8 - 121.2%) -- guaranteed OHKO
252+ SpA Primal Groudon Earth Power vs. 0 HP / 0 SpD Assault Vest Arcanine: 152-180 (92.1 - 109%) -- 43.8% chance to OHKO
0 SpA Primal Groudon Earth Power vs. 0 HP / 4 SpD Mega Gengar: 152-180 (112.5 - 133.3%) -- guaranteed OHKO
252 Atk Primal Groudon Precipice Blades vs. 0 HP / 0 Def Mega Gengar: 236-278 (174.8 - 205.9%) -- guaranteed OHKO
-1 252 Atk Primal Groudon Precipice Blades vs. 0 HP / 0 Def Mega Gengar: 156-186 (115.5 - 137.7%) -- guaranteed OHKO
Note how none of the Gengar calcs even have a boosting nature.
Basically I'm seeing a HUGE weakness to most of the "Big Six" (Xerneas, Groudon, Smeargle, Kangaskhan, Talonflame, Salamance), Geomancy especially. You have NO Pokémon with Protect, offering zero protection from Fake Out, Dark Void, Double-Edge spam, Eruption, Precipice Blades/Earth Power, Brave Bird, etc.
My number one suggestion would be to toss Protect on everything, especially Gengar.