In fairness I don't think the second playmaker thing is a new development and having one at 15 makes a lot of sense but it doesn't have to be. I think there's also the element of always wanting the more 'exciting' player. I think when Ringrose is fit he also can being that bit of playmaking and so if he's there I wouldn't really see the argument for a playmaking 15 for us anyway, especially when Murray on form does a lot more playmaking than most non-French nines.
The issue is more that we're comparing Larmour to the best positional fullback of the last decade at least. Unsurprisingly Larmour has looked better the more game time he gets at 15 the better he looks there and has clearly improved in a lot of areas.
The original point was also about Carbery starting at 15, not as a back up. Still, given he hasn't played there for a good while, I don't know why he would automatically be a 'solid back up'.