When did O'Connor say that? Because there would be a LOT more physical pressure on playing 13 than on playing 12 and he looked like a duck to water playing 13 for the Wallabies. I'd say he might have said 'he prefers playing 10 because it's less physically demanding', but I'm skeptical about even that, he's not been at all shy for Queensland. But even if we assume O'Connor isn't as physical as To'omua, O'Connor is still making compatible post contact meters he's just doing it in a way that might preserve his body...
I would envisage long term (like heading into the 2023 RWC long term) O'Connor shepherding in a new flyhalf, likely Lol'o or Harrison (but could easily be someone else, perhaps the Reds pull a quality young flyhalf out of their ass? not likely). and then sliding into a utility back type role either filling in where needed or coming off the bench. I was a little unsure about O'Connor starting at 10 in test rugby but he REALLY controlled the game really well. He can easily play 10, 12, 13, and probably 15 as well as having quite a bit of experience on the wing too.
IMO right now O'Connor is probably our best option at 10 & 12, and 13 (Jordie keeps this one close, but O'Connor's lines from 13 are SOOOOO good). Should Lol'o (or Harrison) show he's got the right stuff at 10 then I'd slide O'Connor into the centers in a heart beat. But for these NZ games at least I suspect Lolesio will be playing left right out. We are going to need the extra forward and between O'Connor, To'omua & Hodge I think we've got all the versatility we need.