Any method including using a 16" circ could be used, but with that you'd need to change to another method anyway to do the top part.
I don't agree with that statement. In knitting hats, for instance, I use single loop and switch to magic loop for the decreases at the top. I can get down to one or two stitches with my circulars. I use only circulars for these type of things. I don't switch to double points.
The "proper" way, according to the experts, is to knit the hat with circulars then switch to Dps at the top. Who are these experts that tell you that? Usually LYS owners who charge for lessons and materials, or you may find it written in a pattern from a yarn company. They want you to buy from from them. The more needles (including the double points for the hat decreases) they can sell you, the more profit for them. That's my opinion.