Im not disagreeing with you speedo. I also ride a low geared bike or five.
and Im not claiming that TDF riders should ride single speed bikes. (clearly I never said this, though they OBVIOUSLY go to great lengths to minimize weight on the mountain stages- which supports my line of reasoning)
nor am I saying anyone should stay in one high gear and mash up hills. (clearly I never said this)
Im merely trying to make simple and logical a very non-specific question. OP asked "what is easier, heavy + low-gear or light + high-gear". Responses were on the order of "lighter is faster" or "lower gear is easier to ride up a grade..."
All im saying is the more weight you lift, the more work you do.
therefore, strictly speaking, lighter is ALWAYS easier (less total work/energy) on a given hill.
however there are other issues which you point out, including the changing mechanical advantage of different gears, or different physiological concerns. And I agree with you there is a maximum level of efficiency to shoot for when riding - I am a cadence rider and like ~90 RPM
spinning fast might seem easier to the body, but I assure you it involves more energy expenditure due to the compounding effects of efficiency losses with each crank spin, changing momentum of a leg's mass etc.
Seeming "easier" and requiring less work are not the same thing: as you put it: the real world issue of humans riding bikes uphill or whatever it was.
but in a discussion we need to separate all these issues before comparing riding two different bikes up a hill, or else we will not really get at an understanding of the issue.
To summarize my contention:
heavier mass means more work.
therefore:
lighter is always less costly energetically.
however other considerations (mechanical and physiological) can alter the best strategy for a particular rider.
which is to say to the OP: "Until you are more specific with what you mean by your question, and what you mean by "easier", it depends..."