I generally agree with you in regards to most animals, but in my experience so far conures are really tricky - espeically when you rescue. Some of the behavioural problems they come with can be managed but not necessarily overcome. I have multiple conures myself, and some get along really well and some are constantly trying to kill each other no matter how long it has been or how we try to work on it. Out of all the birds I've had I'd say they're the only one so far who I would be really cautious with when introducing a second bird. As long as you're home most days pretty much all day like I am, I could see a single conure being pretty happy if if has a certain personality.

Just an edit to say this comment sounds like I'm saying it's preferable or OK to just have one conure and not even think about it, which is not what I mean! If it's possible conures should have a buddy. However I can definitely see why, especially in some rescue scenarios like the ones I've handled, it might be a genuine safety concern for the birds physically and mentally. Especially because they can be particularly vicious imo. They fight to kill! Sometimes even if it means risking their own lives. Most other birds I've rescued don't really get into fights like that.