Whither Rhydon?

I wouldn't say out of the meta, just overshadowed by Groudon as a Ground attacker. Nevertheless, I still use my Rhydon for the tanky defenders like Snorlax and Blissey with the same moveset like yours. Sometimes, even Dragonite, but Golem does a better job against Dragonite than Rhydon. He will probably become a highly sought-out Pokemon if/when Gen 4's Rhyperior joins the fray.

If any Pokemon doesn't get any love, it's Donphan. I literally don't hear anything about this Pokemon anymore. Once Groudon came along, Donphan was just left completely in the dust. :(

It had its moment with Zapdos and Raikou. It's not terrible against the normal types you mentioned, but with Hariyamas and even Machamps now being a dime a dozen, the only time I use Rhydon is when it is autoselected and I don't bother to switch it out.

No real meta-usage,
not a topp tier DPSer,
fighter abundance,

Makes Rhydon sad.

But hey, gen 4 it will probably be useful again.

Rhydon started to wither from the meta way back at the gym change. They were a big part of the high CP defender requirement of the old system then became a liability when decay set in with the new gym system.

Rhydon is the second best ground attacker. So, if something like Raikou is a raid boss, my squad will probably look like:

Groudon, Rhydon 1, Rhydon 2, Rhydon 3, Rhydon 4, Rhydon 5

Bringing a squad of six up to level 30 is more expensive in dust and candy than developing one level 40 monster (itself expensive). Plus, level 30 and above Rhydon can be had from wild catches without much investment.

I already built up a squad of Rhydon with a mixture of wild catches and powering up, and by the time I get enough Groudon candy and dust to power one up to 40, or four up to 30, another legendary will roll out for me to invest in.

For a best of class mon, I would rather focus on making one best of the best, than yet another raid squad.

I used to use RS/SE rhydon to attack fat normals in gyms, but I have better options for that, now.

Five Rhydon faces will always remain relevant.