Efficiency is always dependent on the variables chosen as your metrics. Burning can be a very efficient way of getting rid of garbage under certain metrics. Burning wood is very efficient in terms of startup costs for heating up an area. Burning coal gas released because you want to make coal coke is materially efficient in thermal output per tonne of coal. I do have to wonder what the timeline would look like if some of the more efficient designs for vehicle engines had been in use all the way back when Benz was starting up.