As someone who wrote the skeleton for the Accelgor analysis, I know it is an extremely niche mon and has a very small niche over other spikers such as Custap Skarm/Forry, which is the ability to beat the two Magic Bouncers while setting up spikes (and Magic Bouncers are super rare in a competitive environment) along with 2HKOing Forry/Donphan and OHKOing Starmie. That sums up its entire niche right there outside of Final Gambit ditch spinblock attempts, and just being fast. Accelgor is extremely easy to play around and it will be forced to use Final Gambit constantly (or end up having to use turns to Yawn>setup spikes as Accelgor is the most predictable lead ever) that barely warrants C-Rank at all as that it has such a small niche to barely even be considered usable in the metagameI completely agree with Terrakion to A+ Rank: It's walled by mons like Hippowdon, Jellicent can easily come in on most sets and burn, so there are quite a few counters. Checks are very common, with mons like Latios and Starmie outspeeding and OHKOing.
I did nominate this earlier but it got swept away in discussion: Accelgor for C-Rank
As one of the fastest mons available, Accelgor can be a great revenge killer as well as a good offensive spike setter that can easily set up a layer or two.
On another note: There are some extra Chlorophyll swepers that need to be on this list. Scarfwynaut mentioned Sawsbuck, who imo should be C>D-Rank as it can function as a nice Celebi/Lati@s lure/revenge killer to facilitate a sweep with RP Landorus on sun teams (btw, RP Lando is actually good in sun, benefiting from Celebi's absence and making quick setup of weakened Scalds and sometimes even Surfs) or synergize well with a fellow Chlorophyll sweeper by taking out Heatran with Nature Power. And even with Breloom, Sawsbuck's SD set is still awesome.
Then there are a few other Chlorophyll mons you would want on the list. First there is Shiftry, which I really don't know much about but I heard Gary2346 has used it and can explain his thoughts here. Dark-type seems to really benefit sun now and could be a solid anti-meta force so I would say it wouldn't be too far of a stretch to put it at C>D. But this is just theorymoning on how viable it is. And for something that I know of well and have brought up before Jumpluff for C-Rank. This thing fixes up so many issues of sun teams its amazing. If you could lure a Steel-type (I think SD Jumpluff being the main set started to catch on already, with the combo of my massive usage of it, my RMT and the analysis) it could U-Turn out with the support set and get a free kill off with Duggy, which can start a Venu/Volc sweep at any time, which is 100% possible thanks to Jumpluff's Memento. Overall Jumpluff is an criminally underrated threat and should be C-Rank. One last point for it, with most teams nowadays getting swept by Volcarona outside of Scarf Keldeo, while sun teams struggle with Lati@s and Heatran to an extent, U-Turn Jumpluff/Volcarona/Dugtrio is an excellent anti-metagame force that can stop a sweep of multiple pokemon and be a significant offensive presence of its own.
And to conclude, I believe Moltres needs to go up to C-Rank. With RP Landorus and HP Ice Landorus-T, Scizor, Techniloom (to an extent) being prominent in the metagame, something that can pose a massive threat off of switching in to those mons (or setting up with Agility) is a huge thing for its viability and with Deoxys-Defense banned and people discovering ways to stop some of those hazard leads, Moltres is starting to become a better Pokemon than it used to be.