The MacBook Air eventually took on the general unibody design of the 11” MacBook, then improved upon it in most ways.
MacBook 2008[0] into MacBook Air 2010[1].
The MacBook 2008 was the chunky unibody that would be inherited by the Pro line. This model had non-backlit keys on the cheaper model, backlit on the more expensive. Only 13", 1280x800.
The Air 2010 had no backlit keys, and 11" or 13", 1366x768. Despite having the better processor it overheated quickly. The battery life was pretty abysmal too.
There is also the MacBook Retina 2015 12" [2]. But this had all the modern amenities.
The MacBook Retina would go on to be killed, but like you said, some of the design decisions would end up being inherited by the Air line.
I guess I got my wires crossed in regards to the Air and the MacBook Retina 12".
[0]https://support.apple.com/en-lk/112512