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Now we're just back to Primordial Sea + Weather Ball.
I'm sorry, but improving Jolteon without breaking it is very hard, for the same reason all Electrics are - they have to be stopped by some Ground-types. Rotom-W is manageable since it's a defensive Pokemon with lower damage output, but an offensive mon that has unblockable Volt Switches will always be overpowered.
You might have noticed the two buffs to Electrics so far don't do that directly, but give them other options, and the other Electrics viable have the same - Tapu Koko gets U-turn which is unblockable but a lot weaker, Zapdos and Rotom-H have secondary STABs which hit Grounds neutrally so they can break past them in the long-term but are temporarily checked by them.
Magnezone has the trapping, and Zeraora has Knock Off to limit the Grounds switching into it. Arctozolt is the one outlier, but it doesn't have a pivoting move so non-Ground answers to it work fine.
well... what would differ jolteon, spikes? thundy. CM? raikou or koko. Sped? zera. trapping? zone. I thought of drizzle actually and give it water pulse instead of surf