>>37209334Koko invalidates all specially offensive Electric types in OU, maybe with the expection of Thundurus-T.
Zeraora does the whole "Electric type attacker" thing better, thanks to that stupidly high speed, better boosting moves, and access to healing and non-Hidden Power coverage.
Therefore, Raikou descends to RU, which doesn't have many good Electrics. There's Mega Amphy, which is slow and also takes your mega slot; Galvantula, which is used for webs more than attacking, although it's ok at that; Jolteon, which is just a worse raikou; and Rotom-M, which has STAB Leaf Storm for ground and rock types.
Raikou dropping will actually be good for NU and Jolteon, since the low ladder shitters who used Jolteon will use Raikou instead, which will not only let Jolt drop, but it'll give NU a second electric type.