I believe that most stall teams would actually run Blissey over chansey because of one thing hazards chansey will be forced to use more soft boiled and be at lower percents because of hazards and yes you can remove them but if you lose defog or rapid spin mon that choice is off the table Corv loses to any special fire attack especially from a ever dominant Zard Y Corv also loses to volcarona which is a demon against stall and finally Corv gets crippled by burn which is run on moltres and scald from toxapex and slowbro. Mega sableye is unreliable in most cases due to losing to either Special or physical Iron Valiant which is a problem for most stall teams and if you miss one read and dont switch mega sabelye in on the hazards then hazards are set up and chansey cant keep up anymore and you cant clean them up further increasing the reliability from Blissey and a stall enjoyer myself I almost never run chansey over blissey because of these reasons. While yes some teams will perfer chansey typically on balance and bulky offense which is why I only nominated Blissey to C+ because of its competition and weaknesses.
EDIT You cannot underestimate hazards and as a stall player myself im surprised you downplayed their importance
As someone's who been active in the developement (and despair) of post-Tera ND stall, this paragraph makes no sense. You are not going to keep Corviknight in on Yard, you are not going to keep Corviknight in on Volcarona (which btw is the freest MU ever for Stall, so I have no idea how you're losing to it), and you are not going to keep Corviknight in on Moltres, Toxapex, and Slowbro. None of these MUs are an issue for Corviknight because it is not meant to be facing these threats: it's supposed to be facing physical threats like Garchomp, Dragonite, or Kingambit. The whole point of stall is that
you have the ability to hard switch walls into threats that your other walls cannot handle. This is why Corviknight was on the standard Chinese Stall pre-Tera ban, as well as a multitude of iterations of stall post Tera ban, despite your so called "bad matchups".
Similarly, Mega Sableye will never want to face off against an Iron Valiant: why should it? You have great options like Toxapex, Clodsire, or Gliscor to switch in, and it's not like Iron Valiant can set hazards anyways, so how is this relevant? As for mis-reading a hazard turn from the opponent, luckily for you, almost every single hazard setter in this tier is a physical attacker, so you'll want to bring in Mega Sableye anyways! Landorus-T, Gliscor, Great Tusk, Ferrothorn, Iron Treads, Ting Lu, Garchomp, and Mega Tyranitar all can be checked by Mega Sableye, so its usually a safe bet to bring in Mega Sableye against these teams. Of course, you'll have to scout sets and keep your Mega Sableye out of 2HKO range, but that's part of playing stall.
Furthermore, you skipped over one of the most crucial matchups for stall currently: the Yard + Gambit matchup. A plague upon all stall teams, this matchup is deadly due to the immense strength of Yard forcing in extremely fat Spdef checks, allowing Kingambit to run wild with the follow-up Pursuit.
252+ Atk Kingambit Pursuit (80 BP) vs. 252 HP / 252+ Def Blissey: 268-316 (37.5 - 44.2%) -- guaranteed 3HKO
252+ Atk Kingambit Pursuit (80 BP) vs. 248 HP / 252+ Def Eviolite Chansey: 195-231 (27.7 - 32.8%) -- guaranteed 4HKO
This damage differential is crucial: it allows Chansey to sit comfortably out of the 2HKO range, while Blissey is essentially crippled after one Pursuit + chip damage. Even outside of the Yard MU, any team with Kingambit + Special attacker can force this unfavorable situation, which is why the ability to tank Pursuits is so much more important than hazards right now.
Are hazards an issue for stall? Of course, and it will forever be something you need to factor into both teambuilding and the actual gameplay itself. But beyond Hisuian Samurott and Mega Diance, Mega Sableye can feasibly block every hazard attempt, and if you let any slip through, Corviknight's Defog at the very least can force in Gholdengo if they have one, and if they don't, clear the field.
Does Blissey still have a place on Stall? Yes, for as long as hazards exist in this game (and Gamefreak doesn't create some abomination of a 2 in 1 item), there will be Stall teams that will favor Blissey for its ability to run Heavy Duty Boots. But currently, Kingambit is the much greater threat, and thus Chansey's ability to eat hits more reliably is valued over Blissey's ability to ignore hazards.
Also I don't know why you keep insisting Blissey and Chansey have places on Bulky Offense: they don't, please stop trying to force the small pink blobs into such a hostile environment, they will do nothing and die and you will feel bad.

to C-