The EV's are maxed out. Both Pokemon have grinded out the Elite Four and Cerulean Cave. I've searched out different Pokemon and used the Bill PC method to see any recalculations, and nothing has happened. I kept both at the same level for this comparison.
The HP stat is derived from the others, so the lower attack and speed stats were going to be what hurt HP the most.
My GSC Nidoking isn't wild exactly, it evolved from a bred Nidoran with a Slowpoke father and a Nidoran mother. I did it to give Nidoking the Confusion egg move. So it isn't exactly random chance with what IVs it got.
Additionally, it was understood in my time that if you captured a "rarer" pokemon in one game, it was going to be stronger than a more common one. I played Pokemon Blue, where Nidoran male are considerably rarer in the wild, so the intuition is that it would be stronger than a Nidoran male caught from Pokemon Red.
Bulbapedia doesn't confirm this rumour, but interestingly it seems like if you have a Pokemon that has a 75% chance of being female, a male has a much narrower IV range. For a maleonly species, the Attack IV is a random integer from 015. But for a 75/25 split species, the Attack IV of the male is a random integer between 1215.
Nidoran male only has a 5% chance of appearing on Route 22...so I want to believe this, that the Nidoran was naturally a lot stronger being caught in RBY.
Quote:
Originally Posted by Bulbapedia
In Generation II games, the baby inherits its stats from the parent of the opposite gender, unless one parent is Ditto, and in that case it inherits the stats from Ditto. The Defense IV is passed, and also either the Special IV or the Special IV plus or minus 8 (plus for values in the 07 range; minus for values in the 815 range); the Special IV has a 50% chance of remaining the same. Attack and Speed IVs are determined entirely at random, whereas HP is determined by the IVs of the other four stats, using the same formula for wild Pokémon. The probability of a Pokémon having the same IVs as its oppositegender parent is therefore 1/512.

Special and Defense are pretty close to one another. So if we're rolling 015 for both Attack and Speed, there's a 50/50 shot of above 7 or below 7. If we assume that the Attack for the RBY Nidoking was going to be 1215, it's a 50% chance of the Speed stat being worse. Which isn't bad at all.
What annoys me about this is it took forever to find out this Nidoking is genetically inferior. Breeding really does suck in Gens 1/2.