Personally, I think you are right when you say they view heroes as saints. Because rn if you think about a hero you won't be like "Oh before he saved he also let thousands of people die." I think 'hero' here is closer to perfect and I also feel like they wanted to comfort Itadori because even tho he thought he could be a hero if he was a sorcerer and he even was somewhat desperate to become one, he killed hundreds when he let Sukuna loose(I know he couldn't stop it but it's clear Itadori still blames himself). Also, I think they wanted to draw a line, like, "being a sorcerer doesn't mean you are a hero" because we know there are countless sorcerers who make a living by killing others people.
Anyway idk where I wanted to go with this little rant, but I hope I made my point of view clear or that I shed some light on the situation...idk
There's... There's just so much about this manga that I like, and so much that just doesn't make sense. This last arc with some sort of death game happening... it just seemed so out of no-where, and weird. The way they treat the concept of being a "hero" seems closer to me as that of a saint or something. "We're not heroes we're sorcerers." I get what the sentiment behind those words in those instances in the manga, in a way, but the actual words themselves just... don't make sense to me? In One Piece when Luffy says he's not a hero, you let it slide. Because he is a hero, his actions define him as such, and he's an idiot, and no-one's going to argue. He's a Pirate, but he's most definitely a hero too. When the sorcerers say it here, being all serious and not actual idiots like someone like Luffy, it just sounds... well it sounds wrong. Cause they are. They save people by killing curses, or they kill curses and save people, it's literally part of their identity as sorcerers. If the curses didn't hurt anyone, these people wouldn't be out there fighting curses. Or at least no-where was it indicated in the story that the sorcerers exist and fight the curses for any other reason other than curses kill people.
Also Megumi's whole "I choose who to save!" thing is laughable to me, because it implies that people who are considered heroes don't do the same. Also I've not seen Megumi once let someone die he could actually still save. Which just leads me to believe the author is a bit confused. To be fair when Megumi first made his appearance in the manga, and said something like that I thought "Oh... he has middle school syndrome, got it." Despite these flaws i do like the story and the characters. Some of the art, the color balance, the layout of the panels, something in all that reminds me so much of Hunter x Hunter, and it's goooood!
But yeah... some "beliefs" held by the characters in this story are just... nonsensical to the point of hilarity. I can't tell you how long I laughed after patchwork face talked about the heart, body and soul. It's some of the funniest overthinking I've seen, and it appears to be done completely unironically, which makes it even funnier. Though to be fair, my confusion could also be due to the translation. I dunno how accurate it is, or how well it was done, although sentence structure seems intact for the most part. So who knows. ¯_(ツ)_/¯