Primal Kyogre A --> A+
Offensive Calm Mind is the set used for this analysis.
Capable of 2HKO on Zygarde-Complete without boosts, possible OHKO with boosts, and guaranteed OHKO on Zygarde before Power Construct takes effect.
+1 200+ SpA Kyogre-Primal Ice Beam vs. 252 HP / 0 SpD Zygarde-Complete: 836-988 (131.4 - 155.3%) -- guaranteed OHKO
200+ SpA Kyogre-Primal Ice Beam vs. 252 HP / 0 SpD Zygarde-Complete: 560-660 (88 - 103.7%) -- 25% chance to OHKO after Leftovers recovery
200+ SpA Kyogre-Primal Ice Beam vs. 252 HP / 0 SpD Zygarde: 560-660 (133.3 - 157.1%) -- guaranteed OHKO
Capable of OHKO on defensive Groudon-Primal, though has to switch in on it or Desolate Land will take priority.
200+ SpA Kyogre-Primal Origin Pulse vs. 248 HP / 252+ SpD Groudon-Primal in Heavy Rain: 1132-1336 (280.8 - 331.5%) -- guaranteed OHKO
Can be OHKOed by offensive Stealth Rock Groudon-Primal, though highly unlikely.
236+ Atk Groudon-Primal Precipice Blades vs. 32 HP / 124 Def Kyogre-Primal: 262-309 (75 - 88.5%) -- 6.3% chance to OHKO after Stealth Rock
OHKOed by offensive Swords Dance Groudon-Primal.
+2 160 Atk Groudon-Primal Precipice Blades vs. 32 HP / 124 Def Kyogre-Primal: 454-535 (130 - 153.2%) -- guaranteed OHKO
2HKOed by Necrozma-DM without boosts, OHKOed by Necrozma-DM with boosts.
252 Atk Necrozma-Dusk-Mane Photon Geyser vs. 32 HP / 124 Def Kyogre-Primal: 180-213 (51.5 - 61%) -- guaranteed 2HKO
+2 252 Atk Necrozma-Dusk-Mane Photon Geyser vs. 32 HP / 124 Def Kyogre-Primal: 358-423 (102.5 - 121.2%) -- guaranteed OHKO
OHKOes Necrozma-DM, but is threatened by Necrozma-DM with boosts due to Necrozma outspeeding. Having a Substitute can allow Kyogre to get the KO.
200+ SpA Kyogre-Primal Origin Pulse vs. 0 HP / 0 SpD Necrozma-Dusk-Mane in Heavy Rain: 343-405 (102.3 - 120.8%) -- guaranteed OHKO
Kyogre-Primal Speed: Base 90, 31 IVs, 152 EVs, 254 Spe
Necrozma-DM Speed: Base 77, 31 IVs, 252 EVs, 278 Spe
CM Kyogre may struggle against defensive Kyogre, as it needs a +3 SpA boost before it can 2HKO. However, it can still easily get the +3 boost if it's at full health.
200+ SpA Kyogre-Primal Origin Pulse vs. 252 HP / 168+ SpD Kyogre-Primal in Heavy Rain: 99-117 (24.5 - 28.9%) -- 99.8% chance to 4HKO
0 SpA Kyogre-Primal Scald vs. 32 HP / 0 SpD Kyogre-Primal in Heavy Rain: 72-85 (20.6 - 24.3%) -- guaranteed 5HKO
With a +1 SpA boost, Kyogre-Primal 2HKOes +1 SpD Gothitelle.
+1 200+ SpA Kyogre-Primal Origin Pulse vs. +1 252 HP / 252+ SpD Gothitelle in Heavy Rain: 249-294 (72.3 - 85.4%) -- guaranteed 2HKO after Leftovers recovery
Kyogre-Primal actually is better off using Origin Pulse on Yveltal than using Ice Beam.
+1 200+ SpA Kyogre-Primal Origin Pulse vs. 252 HP / 4 SpD Yveltal in Heavy Rain: 559-658 (122.5 - 144.2%) -- guaranteed OHKO
+1 200+ SpA Kyogre-Primal Ice Beam vs. 252 HP / 4 SpD Yveltal: 408-480 (89.4 - 105.2%) -- 37.5% chance to OHKO after Leftovers recovery
If Kyogre had just a little more speed, this would matter.
+1 200+ SpA Kyogre-Primal Origin Pulse vs. 72 HP / 100 SpD Xerneas in Heavy Rain: 508-598 (123.6 - 145.4%) -- guaranteed OHKO
Unfortunately (or fortunately), Xerneas does win after Geomancy...
+2 252+ SpA Xerneas Thunder vs. 32 HP / 0 SpD Kyogre-Primal: 352-416 (100.8 - 119.1%) -- guaranteed OHKO
+1 200+ SpA Kyogre-Primal Origin Pulse vs. +2 72 HP / 100 SpD Xerneas in Heavy Rain: 255-301 (62 - 73.2%) -- guaranteed 2HKO
...Unless Kyogre has +3 boosts, which is highly unlikely.
+2 252+ SpA Xerneas Thunder vs. +3 32 HP / 0 SpD Kyogre-Primal: 142-168 (40.6 - 48.1%) -- guaranteed 3HKO
+3 200+ SpA Kyogre-Primal Origin Pulse vs. +2 72 HP / 100 SpD Xerneas in Heavy Rain: 424-499 (103.1 - 121.4%) -- guaranteed OHKO
Overall, I think Kyogre-Primal is worthy of getting boosted to A+. It has too many checks to be S rank, but I don't think A does it any justice.