proposal: lanturn and zapdos
Lanturn is not even on the list. Not exactly surprising, since it isn't used that much, but I propose it should be in rank A/B. It's best as a defensive pivot with volt switch/scald/heal bell/discharge. (variations exist obviously, and icebeam/tbolt/toxic are options)
I think it should be Rank A/B because it can switch into basically every bulky water without worry, since its SpD lets it take minimal damage and healbell makes scald nonissue. It can threaten with stab and volt switch out, giving really strong offensive momentum. The water/electric typing is great because ground types will be scared to switch in.
It also stops raikou, zapdos, and a number of other threats because of its unique typing, the former two being Rank S offensive threats. The reason why I recommend lanturn over other bulky waters is because it has volt switch. It works incredibly on offensive teams needing a SpD core. Can't tell you how many times I've volt switched on an incoming roserade/heracross to something like scarf darmanitan or whatever.
That being said, I also want to propose zapdos fall to rank A. Why is it rank S in the first place? It gets stopped cold by a few walls, has no boosting move, and middling base 100 speed for an offensive threat. As a defensive pokemon, stealth rocks weakness prevents it from walling a lot of threats it is supposed to wall. Raikou is much scarier, and isn't weak to SR.