I'm not sure if there is something I'm missing, but Rock still seems to be a decent type (adv against Flying for dragon/flying and Ice should become more popular with Gen 4). Rampardos has a top 5 attack stat (like Mewtwo level) and good moveset in Smackdown/Rock Slide (is that the best rock set?). Why hasn't there been more discussion about him? I get that he is a glass cannon, but so was Gengar and that had a lot of utility and love.
There has been a bit of discussion about him because of the very points you mention, but I think the reason why people aren't discussing him as much is because he's still unreleased.
It could be months before he's available, and his moveset could potentially be changed before then. They could even go down the limited availability route.
Well its possibly die to it not being released yet and Rampardos' pre evolution, Cranidos being a fossil pokemon which historically are VERY rare in GO
Gengar's very popular for 3 reasons, one, its one of the better mewtwew coutners with SC and even without it hex is still second best ghost attacker, 2, gastly's very plentiful even outside events so its very easy to get, and third, It's freaking gengar, one of the most loved pokemon even before GO (Sidenote, Gengar's also the best ghost attacker despite beign a glass cannon, all ghost attackers are glass cannons or tanks, and gengar's the best of the glass cannons, rarely are glass cannons the best attackers of type unless all of the pokemon of that type are either Glass cannons or tanks, which is how ghost is)
Rampardos might be a great glass cannon, but its going to be extremely rare, that and it is a glass cannon. Most people probably arent too keen on going through the effort of getting a rock glass cannon thats as rare as rampardos will be unless its made a raid boss. Theres a lot of glass canons out there, but aside from gengar they arent overly popular due to being rare or not being popular pokemon prior to go, mean while we all have our SD tyranitar that were so great agaisnt the birds as well as being an already popular and prominent attacker and gen 4 newcomer Rhyperior that are tankier and much easier to get (though are lacking in DPS comparatively) Availability is also a factor in how good a pokemon is. Over all Rampardos is very good, but its not likely to replace tyrantiar
Omanyte and Kabuto have never been super rare. They nest. Anorith from Gen 3 shows up alongside rivers regularly, as does Lileep (which is definitely rarer than Anorith). Only the evolved forms are particularly rare (Cradilly in particular).
Aerodactyl was exceptionally rare (my last non regional gen 1) but then they stuck it in raids.
NEver seen any of them in the wild, even in boosted weather outside of events that is, and haven't seen any since that rock event. likely it will be a 5 k egg hatch, which I believe hast the largest egg pool, so getting good iv ones (which is really all people put dust and candy in) will be a lot harder to get
They're about as rare as starters from what ive seen, they arent ultra rare, but they definitely arent common, meaning its a matter of luck to get a nest.
Dude Omanyte is super common where i live (i always see them going to and back from work in the bus) and as someone said above both it and Kabuto nest so maybe you should check some nesting maps if you need candies. It may have something to do with the biome where you are located, pokemon avaible seem to change depending on that (for example where i live there are no seedots but a lot of oddish, but when i went to a ski resort it was full of seedot and even i got some nuzleafs too)
I live in an aquatic biome, the aquatic fossils never appear there, but a sh*tton of magikarp and even dratini did. (and this is when walking around a park by a lake and filld with ponds/rivers)
I also get they are nesting, but its not like its the only nesting species out there, yes if you find a cranidos nest you'll be set, but if not its going to be a lot more difficult to get candy for them, and with them nerfing weather in gen 4, it will be more difficult to find them (I only ever saw fossils during events outside the rock event when It was partially cloudy, haven't seem fossils outside events at all) because they're nerfing the spawn boosting effects of weather
