Disagree with nearly everything, sorry - Butters isn’t slothful - just off the top of my head he tried to mine enough coal to save himself from being bought by Paris Hilton, he got Biggie Smalls all the way to Satan’s party, and he single-handedly kept Dickinbaus afloat.
Biggest mistake is restricting yourself to “main characters” and forcing him in there at all - he’s so good and pure to represent any sin, much less a deadly one.
I’d also have Cartman as Wrath (Tenorman etc.), and Randy as Gluttony because whenever he’s hooked on something he goes all-in.
Garrison has to be Lust - he’s been closeted gay, out-gay, trans-straight, trans-lesbian and back to gay. All the while being rampantly horny and predatory. Kenny’s a main character but hardly if you get me - you could take him out but you want main characters and he’d have to be Sloth because he has the power of Mysterion and is a big deal in the future but for now he just fucks about with his pals.
Wendy is Envy (“Tom’s Rhinoplasty” & “Bebe’s Boobs Destroy Society”)
Yeah, as someone else pointed out, the better post might have been to just have 7 Cartmans as a joke but this was your idea and you did ask for thoughts.
Envy could also be Timmy in his Scout Uniform from Cripple Fight