alice writes:

Duh.No one is arguing that a jet uses less fuel up high.It is the
reason why that is in question.You are making a HUGE misconception
about the reason why.

Less fuel = less power.

By your reasoning, A jet would never have a service ceiling!

Jets have a service ceiling for several reasons. For one, eventually
the air is too thin to provide any lift, no matter how fast you are
moving. For another, eventually the air is too thin to support
internal combustion engines.

Explain to us what a "sweet spot" is.

Greatest distance covered per unit of fuel consumed, lowest wear and
tear on the aircraft (especially engines).

Why is it that you feel the airlines dont take into account TIME
when doing the preflight planing.

They do, but fuel costs more than time. That's why flights are longer
now than they used to be: airlines plan for fuel economy, not speed.

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