Basically, I've come to see exploders a lot more sufficent for the "omg last chance gotta kill that Exeggutor" shot. Golem can kill Exeggutor. Rhydon doesn't. Rhydon is a powerhouse, however, and perhaps with a mixture of Chansey, Alakazam, Hypno, and/or Exeggutor, to paralyze/special absorb, he's pretty dandy. You have to be pretty damn precise to try to predict with Rhydon, however, since the misprediction can lose him. Basically, he's a heckova lot more risky than Golem is, but hey, is can work from time to time.
Though I'd like to adress something Jackal said about Rhydon:
1) All they have left is chansey, you have starmie (or a random sleeping pokemon or something) and [golem or rhydon]. If its golem, you win bar an ice beam critical hit becuase you can explode, rhydon has to settle for hoping for a bslam para. This situation also works for something like eggy/snorlax, even a paralyzed tauros. Explosion is AMAZING. I cannot stress this.
You used Starmie as an example. If this is the endgame with Pokemon like this, one would think that Chansey would have some status ailment against her. People fail to realize that if Chansey gets fp'd at the wrong time against a physical attack, she's dead. If one can paralyze her (in this case with Starmie), one can easily switch to Rhydon, since I don't precisely think that they'll use Ice Beam. If you didn't want to risk prediction, it's not that much of a problem, as Earthquake 2ko's no matter what just like Ice Beam. The exception is if they critical hit. Golem means sure-fire win with a paralyzed chansey, but Rhydon is pretty damn manuverable in reality.