I agree with mamoswine for b+ it just has a hard time ever switching it and is usually pretty easy to wear down or revenge kill. Skarmory also walls it more often than not and porygon2 can deal with non super power sets.
blissey is probably better than chansey in our current meta because of its use able special attack
swampert and breloom are both pretty viable in the current meta i think b+ is fair for both of these
I think c+/b is fair for smeargle when it works it works well
i think tentacruel is being severely overestimated, if you look down the list of ou mons it has very few if any safe switch ins that arent another bulky water and even those threaten to burn it with scald and help wear it down. Both cofagrigus and certain gengar sets are able to spin block vs it so it cant even reliably spin, where as spin variants of starmie are much harder to spin block against.It checks/walls certain volcarona sets but to be able to stop them all it needs haze, it has a decent matchup vs certain hydreigon set, and it can annoy some other bulky waters but even less so now that milotic carries flame orb more often than not. I just cant see this pokemon being anywhere past a b+ ranking, it just doesn't really do anything that well in the meta.
I think all four of the bulky waters belong in the same b+ tier starmie/milotic/mantine/tenta all bring something to the table that the others dont and dont think you can definitively say that one is better than the others because they all are better in certain matchups.
venomoth should probably be around a b ranking it has some different traits than volcarona that enable its setup like disable/sleep powder and with tinted lens it can usually get by with just 1 attacking move.
Kingdra should drop to b+ all versions of it are stopped cold by ferrothorn and the special rain variants are dealt with by chansey/blissey and spdef variants of mantine/milotic, outside of rain this pokemon is very mediocre and unboosted speed its often just ohkoed by faster offensive threats.
I would also like to nominate darmanitan for A- ranking as it can pretty much 2hko the entire meta and sits in a pretty decent speed tier
Reuniclus/starmie/breloom/kingdra/conk/hydreigon can all switch into milotic on offensive teams although some may not appreciate a rogue icebeam and breloom probably wants to have its orb activated. It does win 1 v 1 vs about half the tier but it will also get 2hkoed by a ton of offensive mons if its forced to switch into them.