This is getting kind of off-topic, but one underrated thing about Gengar is that it helps back up Chansey against Lapras.
Back on-topic, Gengar is rightfully OU for RBY in these rankings if we're still going by that objective metric. It's not doing the heavy lifting for a team the way the big 4 are (or even some "normal" OUs like Lapras and Alakazam), but the sum of the little niches and situations where it's immensely useful is pretty substantial.
rightfully ou of course, but how is he on the grander scheme of things? i propose a methods of going about determining some sort of objectivity: one giant "viability" ranking, where each pokemon can have up to 5 different entries for each of its gens. then we determine some sort of scoring system for each tier, either flat or variable, then just total it up. e.g.
S. GSC snorlax
A. RBY Tauros, RBY snorlax, Adv Ttar
B. GSC Zapdos, RBY Chansey, etc
alternatively, we can give these tiers different names and have each person chime in on which poke/gen combination belongs where. going back to jellicent's original suggestion, but adding more tiers.
1. GSC Snorlax tier
2. dominating OU tier (hopefully just 1 per gen, maybe 2. this is the best of the best from each gen)
3. 2ndary but still dominating OU (should be still S ranks on most versatility lists. whatever remains from jorgen's top 4 lists basically)
4. versatile OU stuff, ubiquitous pokemon (unquestionably A ranks should fall here)
5. pretty good but starting to get nichey stuff. but still unquestionably OU pokemon (lower parts of A, but mostly B rank essentially)
6. mostly metagame dependent stuff; situational at this point (hopefully we're still in B rank)
7. banned pokemon
8. non-existent
9. non-ou (although i think if you don't show up on any of the viability lists, it should count against you)
obviously it's going to be more saturated as we go down the rankings, but ideally we weed out shit pretty heavily in the first 4 ranks to figure out who's who. we want to reward a pokemon for being DOMINANT, instead of giving everyone "ehh he was there" points. so something like snorlax/ttar would benefit from this particular emphasis.
alternatively, you can reward consistency by making less tiers. e.g. dominant -> ou -> not-ou, and something like starmie/gengar/zapdos would benefit more here.
basically, do we care more about MVPs or all-star team appearances?