Standard RBY and no Snorlax is incompatible. Snorlax and Tauros are the only things that can threaten every switch without explosion. Thats why they are one step above the others. Every team needs Tauros/Snorlax to be standard, then it almost always has Chansey. Chansey is not as necessary as Tau/lax but if we are talking about standard team, then Chansey is in for sure.
Standard team(s):
Lead. Alakazam / Jynx / Hypno... Anything meant to (try to) take the sleep. Zam is usually the best at that due to how does he match up vs common sleepers. And recovers. Not better than chansey though, but chansey is much better at otehr things. Obviously.
Snorlax. Both SD with Surf/HBeam/tbolt? (who uses cloy, but cloy 100% walls para snorlax, just saying) and Reflect/Rest sets are standard. The later capitalizes on chansey forever (reflect so that you can stay in when sleeping vs the things that would threaten your switch-in), and the former is usually looking for a 2 on 1 trade.
Tauros Self explanatory
Chansey TWave + tbolt is the standard
Lapras / Starmie / Alakazam. Sing Lapras unless you have lead sleeper. Starmie with Hydro Pump or twave sets. Lure out Chasney and go to lax/tau. If chansey is out, sweep.
Exeggutor / Golem / Rhydon / Alakazam. Eggy with stun though d-e can beat para zam/jynx in switches to allow eggy to go for the sleep on chansey. Otherwise you ideally explode on it to open up the water. The rock capitalizes on para'd chansey or zam and walls random electrics. Without free switches they aren't that good though, especially don, who can't explode. and if facing Eggy and Starm, forget about doing much.
As for ranking the rby pokes
1- Tauros
2- Snorlax
3- Chansey
4- Eggy / Alakazam / Lapras / Starmie
5- Rhydon / Golem
6- Slowbro / Cloyster / Zapdos / Jynx / Persian / Gengar etc
Snorlax and Tauros are the only things that can threaten every switch without explosion. Thats why they are one step above the others. Snorlax is much more consistent and versatile. Tauros just makes switching out the worst option in most cases. A switch usually means Tauros can do at least +-80% damage before being hit.
Chansey walls the special side. It's interesting to see how all the offensive strategies start around Chansey, as it's an almost pure defensive poke. It walls waters so you try to lure it out with them; take out chansey, then sweep with your Starm/Lapras; Chansey forces eggy to boom, who is indeed trying to explode into it to open up things. Physical stuff always thinking on capitalizing on Chansey to get free switches (and on zam to some extent but zam is just a mini-chansey after all). etc
Eggy is probably 4th. Its a pretty good defensive and offfensive pokemon with good defenses and resistances and explosion to ko chansey, and sleeps and stuns.
Lapras and Starmie are also pretty good and match up decently well vs physicals. Walled by Chansey (though lapras can still sleep or even go with cray, and both freeze). On the other hand, waters can lure out chansey so that you can get the lax vs chansey matchup; and Chansey allows Restlax to sweep forever unless there is something threatening a resting snorlax with reflect up AND you (i.e zapdos, cloyster, bro). Lapras is probably better tha starm overall though, but Starmie is the perfect wall for Cloyster and Slowbro.
Rhydon/Golem aren't really that good as many people may think though. They are mostly ranked here due to how good zapdos would be otherwise. Look at the common pokes and match up don/golem vs them and youll get much more "bads" than "goods" vs them. They are very good at capitalizing para chanseys and para zam and para in general, but eggy or starm gives them a lot of problems. At least Golem explodes which is very very nice.
Alakazam: REFLECT. It's the difference between being a threat and being not.
Persian in probably worse than it should be because there are infinitely more gars around than it should. Gengar is like a special Golem without [double] STAB and a less powerful explosion. And you know that Physical>special. Gengar just matches up bad against everything that is not a water. Ok Gar sleeps but who cares. You already have Eggy and/or Lapras. Sleep with one of them.
Two potentially dangerous unexplored pokes: Victreebel and Kingler. Probably better than gengar. Jolteon is an overall inferior zapdos though it capitalizes on waters much better.