I shall try to help
Groudon-Primal
This is good but the EV spreads seem really weird. There is probably a reason behind it but I have no idea so I think you should have max HP and max Atk with the rest in Sp.Def.
Deoxys-Attack
Maybe you could use a Life Orb to get more power on both sides. I cannot change much.
Xerneas
I would change Substitute for Grass Knot since Groudon can wall you and OHKO with Precipice Blades. Also helps against Kyogre.
Yveltal
This is good but maybe you could get rid of Dark Pulse for U-Turn. This also has weird EVs so just remove the HP stats and put it in Atk or Speed
Arceus-Electric
I actually think you should change this into a different form and make it your support mon. Here's a set I think would work well.
Arceus-Water @ Splash Plate
Ability: Multitype
EVs: 252 HP / 248 Def / 8 SPA
Bold Nature
IVs: 0 Attack
- Judgement
- Recover
- Will-O-Wisp
- Energy Ball
This set works great for me and it's pretty good for a physical sponge and you can put Light Screen to make it more bulky on the special side as well.
Necrozma-Dusk-Mane
I think you should replace Outrage with Dragon Claw and replace Earthquake with Dragon Dance. Also go for Max Attack and Max speed with remaining in HP
I hope I helped
