Limiting each Rank to some ratios might be helpful, but it would also restrict viability analysis greatly. That said, some Pokemon in B Rank do not belong there (Rhydon), and eventually a similar ratio might be found.
I want to move Rhydon from B Rank to D Rank. While it is a palpable SR user, it is also not very good. Firstly, it has no recovery because most of the time it is forced to run Eviolite or Choice Band (usually the former) in order to be effective. Secondly, in contrast to some Pokemon, Rhydon does not have Sturdy and thus is OHKO-able (especially from the Special side) before it can even pull off Rocks. It does not get Solid Rock to fix this; its Dream World ability is Reckless (which is not helpful since Rock Head is generally better anyway, but Rhydon's movepool is found wanting to make either ability useful). Thirdly, Rhydon's analysis itself admits that while it has potential, it is also outsped and killed by 3/4th of the tier. It also admits that Rhydon is "high risk, high reward" (which means at best it is C Rank; many Pokemon present in B, C, and even D Rank generally have significantly less risk than Rhydon does).
Some of the things Rhydon could beat also check most of its sets. While Poliwrath does not lose to Rhydon regardless, it finds OHKOing defensive sets with Scald not possible (what about with Waterfall, though?). Other than Choice Band Rhydon, Tangrowth beats most of them. Steelix also can check Rhydon, albeit it is shakier because CB Earthquake can 2HKO. Priority attacks from Kabutops and Feraligatr, to name a few Pokemon, also shut Rhydon down. Choice Scarfers of base 70 and above also laugh at Rhydon (even Primeape!). Many Pokes that also just naturally outspeed Rhydon (if it isn't using the equally-situational Rock Polish set) also just outspeed and check it (Crawdaunt can outspeed all Rhydon, for example, and OHKO with Waterfall).