Snorlax does offense better than Zam does defense. You seem to be under the impression that RBY is special dominated [as per so many guides state]? It's pretty balanced. Zam's defense is not so good, nor is Chansey's once people see that. Reflect zam beasts, but other zams are pretty non-threatening. That's not to say they're not good, or necessary even, just that it's not the unbreakable what have yous. This feels like Skarmbliss all over again. Is RBY really that new to people?
I don't think Snorlax is anything like Rhydon. Apart from something odd like Aerodactyl, standard Snorlax doesn't need to necessarily run away from anything. And it has a 390 base power failsafe. Not to mention, when shit's para'd, lax is on par with Tauros. It won't win you a lost game out of the blue like Tauros will at times, but it'll win you games. Consistently.
If one is using Snorlax as a replacement for either Zam or Chansey, Lax wont last long to really break through defenses as it should be.
That seems like a general assumption rather than a statement of fact. Have you tried? You'd be surprised.