This article discusses "dry insight" or vipassana without jhana. http://www.vipassanadhura.com/jhana.html
The article makes some very good points, and it is true that the practice of insight/vipassana without jhanic concentration is very valuable. We know, for example, that in the medical community people are being trained to implement insight meditation without jhana for pain management, PTSD alleviation, and many other purposes. To require jhana before experiencing insight would put this practice on a high shelf that few laypeople could initially reach.
But, I'm going to stick to my guns and suggest that jhana itself is expressed as the atom (carbon, for example), with samatha as the nucleus and vipassana as electrons ....I believe that Ajahn Geoff may have expressed it as being like a bird with only one wing, flying in circles...the two wings of samatha and vipassana are the elements of jhana, and cannot "fly" correctly without each other, or operate fully independently of each other.
A technical distinction to be sure, but it seems to me that when the Buddha admonished "go, do jhana," the task was for the monks to cultivate this practice at its most complex form, and the form that places one on the path to release. YMMV.