Well, yes and no.........comes from using the hood, not much if any benefit at all from the compressed insulation on the down side. If you used a JRB hood or a Bozeman Mtn Balaclava with the bag quilt-style, I don't think you'd see much difference.....
YES I have separate hoods and balclavas ( hooded PG jacket, thick Patagonia Pile balclava, neck gaitors and even a 3" thick gore dry loft Marmot separate hood!). I have almost always used one or more of these when trying to use my bags quilt style below 30*. Virtually every time I found myself too cold, getting in the bag ( often after removing some of my warm clothing and/or hoods) and zipping up, sealing the neck collar and cinching down the hood to a breathing hole, I would be more than warm enough pretty quickly. It really was never much of a contest. In addition, my back, which had not been actually cold but not actually warm ( I would mainly be aware of discomfort on top) would now also get an actual "warm" sensation pretty quick.
But, keep in mind, this is trying to use a mummy bag as a quilt. The seal and draft around the neck and shoulders and sides- especially when I turn over in my sleep- is just no good compared to being zipped up in the bag. However, I'm pretty sure a quilt- designed to be used as a quilt from the get go- would be quite superior in being able to prevent these drafts. Thus if used with any of my hoods would probably be a-ok. Though I still doubt it could quite match the draft proof seal of a mummy bag's hood/collar. But it should be pretty close, I imagine. And much more comfortable and easy to use.
NO: I don't think so regarding back warmth of either a quilt or down bag vs a synthetic bag. The test I am reporting has nothing to do with hoods or drafts. It was the same in both cases. With the bag used quilt style( or any other quilt and probably a down bag), the only insulation between me and the cold air is the nylon of my hammock. When I got in the bag for the test, I did not zip the bag up nor put the hood on. If anything I had less coverage now on top than I did quilt style, because I was fully unzipped on one side. But there was an almost instant and significant improvement in my back comfort/warmth so that I could have stayed there all night if needed.
No, I don't think the dif ( in this bck yard test ) had anything to do with hoods or draft prevention. It was that layer of PG under my back, combined with whatever benefit was contributed by the bags wind/water resistant shell. Or so it seems to me, but I might be wrong.