Thoughts: Char-Y for A+
The first of my reasons for this, that I noticed upon skimming the past few pages has not yet been mentioned, is an average speed tier and lack of a relevant Speed-boosting move (barring Dragon Dance... hmmmm), meaning after switching into a resisted Fire Blast, a number of threats can force it out with the threat of super-effective moves. Sure, nothing save the blobs is repeatedly switching into Fire Blast, but surely, any reasonably competent player can make sure it does not get to repeatedly switch in? It cannot be overstated how crippling a 4x Stealth Rock weakness is. It means that as long as it stays active, Char-Y can only switch in twice. Char-Y can easily use Roost, but this is a move that forces it to lose momentum, as Roost turns can be easily predicted and be capitalized on by the opponent, especially if he is using an offensive team.
Speaking of team archetypes, both offensively and stall-oriented teams aren't threatened enough by Char-Y for it to be S rank. Offensive teams can handle Char-Y with hazard stacking, deosharp, and simply having at least 4/6 team members faster than Char-Y and 3 of these who have a move that can take away >50% of its health. The only situation that Char-Y threatens offensive teams is if it manages to switch in against the remaining 1-2 slower members. Balanced teams also frequently contain members like Garchomp, Terrakion, and (Mega) Tyranitar, things that can be aggressively double switched in against Char-Y, or that can take a Fire Blast if necessary, and proceed to reverse momentum.
As for defensive teams, I'll just start by saying that (as with all good stallbreakers) Char-Y massacres all common members of such teams bar like 2 in Latias and Chansey. Does that make it incredibly threatening to these teams? Perhaps. Char-Y is doing 29-34% to Chansey, and 35-41% to 252/0 Latias with Timid sun-boosted Fire Blast. This would destroy stall teams, if not for the fact that Chansey and Latias both have access to reliable recovery, and that Fire Blast has a whopping 8 pp. Once that pp is expended, the Char-Y user is essentially down 5-6. If anything, Char-X is the far more threatening stallbreaker with Dragon Dance, Flare Blitz, and Outrage, in addition to being a great sweeper / cleaner (hence comparing the 2, I feel there is a marked difference in how good each Mega Char performs in the meta - a difference that puts Char-X in S and Char-Y in A+). All this does not make Char-Y weak, rather, it means that it is not as massively threatening as people hype it up to be, and that A+ seems like a more reasonable place for it to be.