Nidoking does not do it better. Squirtle is the fastest.Pretty sure the tier list does not count 'solo the game by itself'.
That's not mentioning how Nidoking probably does it better
And if I can have a Pokemon that I get as a starter cover the entire game without any help needed other than a couple of E4 pokemon (mostly for efficiency's sake), how exactly is that not a positive trait when considering in-game tiers?
It gets an A in every category, as well as an A++ ubergod grade in Matchups, since he doesn't even need any support (which is the point that you said doesn't matter, which doesn't make sense).
-Availability: Can you get them early on and are they easy to get?
-Stats: Do they have a usable stat distribution?
-Movepool: Do they have a good movepool that needs little TM support? (By that I mean hard to replace TMs such as ones you get from gyms.)
-Power: Are they strong enough to sweep through enemies without taking too much damage in return?
-Type: Do they have useful STABs and resistances?
-Match-ups: Do they fare well in gym and/or boss battles?