Even with the crippling grass and water weaknesses, rhydon's sheer bulk just cant be overlooked. Rhydon is actually the most physically bulky pokemon in the whole game overall when you take eviolite into account, and it can also take its fair share of hits from the special side. Rhydon is actually capable of taking things like STAB waterfalls from kabutops with the correct ev spread, and can also take hp grasses from things like moltres with a specially defensive spread. Rhydon is very flexible with EVs, and its easy to spread them across its stats to get the desired results you need. Also, while rhydon's typing might not be the best defensively, its certainly great offensively, edgequake coverage is nothing to laugh at, especially when you have STAB on both rock and ground, and have a base 130 attack to use it with. Rhydon also packs megahorn to hit tangrowth with if you have good prediction skills. As i said before, despite rhydon's weaknesses, it can take a fuckton of punisment on the physical side, being able to hard counter things like absol and zangoose with a physically defensive spread. While also full stopping CB entei and being able to check kabutops lacking waterfall (basically all of the ones with rapid spin, lol). Basically, if you dont have a STAB waterfall or power whip and your a physical attacker, rhydon can check you. Also, a calc to show just how bulky this guy is.
252Atk Choice Band Pure Power Kyurem Black (+Atk) Outrage vs 252HP/252Def Eviolite Lightningrod Rhydon (+Def): 80% - 95% (334 - 394 HP). Guaranteed 2HKO.
If you didnt read the above calc, thats banded +2 kyurem outrage vs max/max rhydon, this nigga is bulky.
So TL;DR: I think rhydon should stay in B, its sheer bulk, power, coverage, and stealth rock more than make up for the flaws it has imo.
16:46 <TLCNU> Esca literally is 2HKO'd by Stoutland Fire Fang
10:33 skylight molk put me in your sig