That data is pretty useless, as the two machines had quite different specs and price points. The Air didn't even have a Retina display for most of the MacBook's life. Also, the Air was cheaper even though it had a bigger screen.
But there is good data from the time when there was an 11" Air.
Agreed. The 12" Macbook was positioned so poorly in it's limited run that it's almost completely meaningless to try and use the sales statistics to see how well a 12" machine would do again (and you're right, the 11" Air sales figures would probably give a better idea). The naming of the lineup was confusing: MacBook Air, Macbook, MacBook Pro; the pricing was a deterrent, and also the justification unclear to your normal consumer; and it was made poorly, having several huge handicaps (awful keyboard, single port, underpowered).
Yes, us folks on this forum can understand from a technical and business point of view why it was manufactured in that way, and how the price point came to be, but a lot of people just didn't want extreme portability
that much.
Now, if the 12" resurrection was done in a way that makes sense, I'm sure it'll be a great hit. And you simply can't prophesise that it wouldn't be a hit, based on the previous attempt that was done in a way that simply didn't make sense.
For instance, lets say that the current 13" MacBook Air reduced its shell size, and had some other fancy redesigns to allow it to come in at 1.1kg, with pretty much the same specs and performance as the current MacBook Air. And lets say they also released a 15" MacBook Air for people who want more screen real-estate but don't want the Pro (a lot of people want a Macbook simply to have almost permanently wired up in their home). Assuming that the 13" MBP is discontinued (not saying it will be), the lineup looks like this:
13" MacBook Air: $999 (1.1kg)
15" MacBook Air: $1,299 (1.4kg)
14" MacBook Pro: $1,999 (1.6kg)
16" MacBook Pro: $2,499 (2.1kg)
Yes, this is just a hypothetical, but the point is that in a situation where it made sense, i.e. a lightweight model was released without huge compromises, in a clearly defined lineup where the model is positioned well, I think it'd be a huge success. Or of course, the above could be done but with the Air being a 12" / 14" choice with white bezels and a range of different colour shells, and the same price / weight as above.