The thing is its out done by kyurem and lele, and its a ground type that does not do what a ground does, which is defensively check electrics throught the game which nidoking cannot due to lack of bulk and lack of a recovery. Lando-t does not switch in on nidoking at all, especially if it is defensive and has not scouted for ice beam yet, that is so dumb to do to leave ur lando-t on a nidoking. The Cons of nidoking is that it just straight up does not do anything defensively, and is all or nothing unless provided ample support from teammates via pivots, pokemon to defensively counter what a ground was supposed to do, and hazard and paralysis support. It justifies B as it has way to many flaws to be reliable pick on a team and being to hit or missNidoking is completely fine in the current metagame IMO, and B+ rank is completely fine. If anything, I'd argue for putting it higher, due to it's sheer offensive potential. One common sequence with Timid Nidoking is that defensive lando swaps in, you see that it's probably a defensive variant, and then you can throw off a free ice beam and you've got a fantastic position. Looking at it's compatriots, we mostly see huge threats that unfortunately have something holding them back- in Slowbro's case Slowking, Dracozolt because it requires sand, Bulu due to Rilla. This feels accurate for Nidoking, as it can provide shocking offensive power, but at the cost of a ehhh speed tier.