When I brought up Lando-T, the main point I was trying to emphasize was having to sacrifice either Knock Off or Toxic for Stone Edge and not Physical bulk for Special bulk bad writing on my part. And as for Pex, it has to run SpD Haze which admittedly isn’t too big of a sacrifice although it does still have a more difficult time checking some potent Physical threats.Spdef Lando has utility beyond Volcarona like Koko and Pex runs mixed spreads for scouting Dragapult pretty much constantly (max physdef is a waste of evs), nothing is lost from these pokemon attempting to check Volcarona. They're also far from unreliable as well given a Volc cant be both offensive and Bulkarona at the same time. you can easily adjust your gameplan by working out the volc variant at preview, since Bulkarona allows for more offensive counterplay overall via a reduced speed tier and offensive volc is so reliant on teammates paving the way for it to be able to handle its many checks. its not like its just them, Urshifu Rapid, Blissey, Garchomp, Dragonite, Heatran, Unaware clef, and other random stuff function as fine checks or counters to both sets.
As for Weavile, i wasn't suggesting this. I was saying that both of your examples for pokemon that Weavile pushed down are incorrect or at the very least had plenty of other factors contribute to their downfall. Slowbro started dying off pretty much the second Ace went and Rillaboom is an rker to Weavile if anything, given it needs solid chip to kill with shard and not die to Glide. Toxapex rising was inevitable regardless given its an infinitely better wall than Slowking and the metagame is very cruel to futureport reliant builds atm with stuff aside from Weav, like Kartana, Mew, Hazard spam, and just a general inclination towards a more offensive pace. Tapu fini did rise partially due to the rise of Dark spam though yea, same with Wole, but good pokemon rising to cause a disrupt in the meta isn't grounds for viewing them as bannable. I know you didn't say this and i'm sure this wasn't the intention but honestly that's what putting Weavile here feels like to me, a pokemon that rose up to disrupt a common trend and so new trends arose to combat it.
I mentioned Weavile partly out of bias to be honest, it’s one of the most fun mons to use for me. I admittedly jumped the gun on this one since it is a fairly new beneficiary of the meta and I didn’t give the meta a fair shot to adapt.