OP, yes you are right the new Pro (without DVD drive) is much lighter and thinner and quite comparable to the Air. The Retina screen is definitely better but you do need to see them side by side to tell. The Pro is more powerful computing wise and you can get better spec ones. The Air is “de-tuned” to reduce power consumption and give better battery life.
We recently did a side by side and went with a Pro. Mainly due to the screen but also a view that it would be more robust than an Air. If you are not budget concious then I think the Pro is the obvious choice. I suggest you get 8GB RAM and a 256 SSD min. There are rumours of a retina 12 Air which would be a nice machine and make the choice even more difficult, however that would be a 2015 machine now.
The prior generations of rMBP’s had spinning drives, perhaps that what the posters where referring to