Only foil coil immersion types. Our "kettles" over here have enclosed heating elements under the kettle, so it would lose a bunch.
Immersion heating elements are about as efficient as one can get.
We used to place a few coiled rubber bands between two spoons, and hook 'em up, and that would boil water pretty quick too.
Gives "Direct Current" a new meaning.
Most "plastics" that can handle those temperatures also conduct heat pretty well.
Stick a lid on it. Once the water is boiling, one can reduce heat and retain boil, another good reason for gas.
I love finding uses for wafting, otherwise wasted heat.
A smaller "vat" has less exposed surface area, and is quite valid to consider as a spoiler to your claim. It all comes down to using the right heated pot for any given volume considered.
Why do you think solder pots are short and squat, and not some eight or ten inch diameter device? It isn't just the handling issues. It has a lot to do with conservation.
When I put water on to boil, I start with *very* low heat, and most of it hits the mark, and that which wafts, heats those same sides. The flame barely leaves the burner head, and the gas meter barely moves, and I boil water much better with a long slow process than a "stick a torch to it and GO" method, so not much "spills" up the sides.
I am very lean on consumption. My carbon footprint barely exists at all. Been riding a bike to and from work for the last twelve years.
Gas is definitely the best, most controlled application of heat, therefore is the best way to cook.
I wish microwave ovens were wattage controlled, instead of duty cycle controlled. I would have many more uses for it then. Still, it is my second choice. Electric burner stoves, and cooking accessories are the most wasteful use of juice there is. The only proper electric stove would have skillets, pots, and pans with integrated elements in them.
Otherwise there is a lot of loss with electrics as well. I'll take gas any day.