first off, ty for the link, but I didn't see any arguments for any particular ranking. Was enlightening anyway (I might post my own vap set on that thread in a bit).It also lacks physical bulk if not invested. Here is the link to the vaporeon discussion.
Second off, saying it lacks phys bulk if uninvested can apply to a decent variety of pokemon who are fine on the phys side. Florges and chansey (yes I know chansey is OU) also lack physical bulk if they don't invest in it, and yet they both have plenty of phys bulk. Vaporeon has decent enough special bulk that even uninvested, it can still tank what it needs to. Also, many viable special attackers are either mixed or pseudo mixed (psyshock or secret sword) like almost all psychic types, Tornadus, and a few others, making that mixed bulk all the more desirable. Especially with chansey out of the picture, I think vap makes a perfectly viable mixed wall.
That being said, I think it's prolly fine in B+ due to Jellicent being in the same tier. Jellecent and vaporeon have a lot of similar strengths and weaknesses. Jellecent has the advantage of WoW, better typing, and reliable recovery. While Vap has the advantage of phazing and fat wish passing. While I am still scratching my head as to why they are both below tentacruel, I do not see any differences in relative strengths to justify putting vaporeon above or below jellicent.