Is it poor, or is it more of that it doesn't fit into your narrative? I think it's a great analogy, but that might be confirmation bias eh doc?
The point at hand (of which the analogy tried to draw a parallel for some better/deeper understanding) is that the gas is a part of the fuel which allows the engine to run. Much as the "elements" are a part of the fuel which allow the plant to grow. By saying the elements aren't "used" by the plant is hard to understand what you mean because I think that isn't exactly correct to say that the plant "converts" but doesn't "use" wtf is the difference?
The engine converts gas to mechanical work but doesn't use gas... mkay if we're playing semantic game then you better be ready for onslaught of policing of everything one says