The first point is true but frankly with pokemon like Heatran and Victini being a thing, its usually not that difficult to find the room to hard swap something in and get some damage going. Torkoal not being able to pivot is definitely a downside, but I think you're overselling how much it matters.
Second point is true but I do think it's unfair to discount Torkoal's utility in the possibility to have Rocks+Spin, absurd bulk ( 252 Atk Life Orb Garchomp Earthquake vs. 248 HP / 252+ Def Torkoal: 242-289 (70.5 - 84.2%) -- guaranteed 2HKO, There are neutral pokemon who take more than this), lava plume's sheer obnoxiousness, Body press' ability to snipe Tyranitar, etc. It's an incredibly varied setter and I've been surprised by its movepool and sheer bulk time and time again.
third point is also true on paper but then you think of the list of pokemon Sludge bomb hits, and the list is pretty much just Lati twins, Kyurem somewhat harder (which is fine because its so easy for Sun to maintain rocks), and a few random midgrounds. There really isn't a lot of pokemon you strictly lose to because of Sludge Bomb being so much harder to fit., EP+Weather Ball+Giga+Growth is great coverage.
this one feels really random? weakening Urshifu-r is fairly relevant I'd say. Not like Heatran is a non threat to Rain either bc of Toxic and the possibility of rocks.
This ones more of a case of differing gameplan than anything, Rain's sweepers kind of need that pivoting because they can't even dream of matching the destructive power of a Growth Venu, especially Kingdra. Plenty of good Sun breakers offer pivoting, most notably Darm and Victini, and defensive pieces like Mandibuzz can do the same. I wouldn't say one is that much more linear than the other really.
Same deal as what I said before honestly, There's more variety yea but Rain wishes it could get a sweeper as devastating as Venusaur, and there's still quite a few pokemon that benefit from Fire coverage being boosted (Hydreigon, Garchomp) or that just appreciate the raw power sun allows them to have (Victini, Heatran, Darm, Volcarona, even Blacephalon)
This is just not really true, Rain this gen is definitely fairly reliant on its weather being up, most of the pokemon on the archetype are either severely crippled without rain, like Thunder users, or flat out just really really bad without that support, like Barraskewda. I wouldn't say its that far off from Sun really.
in fact, I'd go as far to say that
and
are worth a raise to C+ or
and
are worth a drop to C+ (i think rains C lol but i wont push my luck), these playstyles are not an entire 2 subranks apart in viability and if anything, i consider Sun better