Gettin' a bit confused here. (nothing new in that)

In the big sprawling thread I started down below, there's been a couple of
themes that have come up.

One is that I am pretty sure that for the same IAS (not TAS) at a higher
altitude, more power is required. However, one contributor to the thread has
stated that this is not the case:-

"Power is net force time velocity. Thrust equals drag, net force is zero.
The energy change of the airframe overtime is zero. All energy from the
engine is going into the air. The power to move air to make the same thrust
is the same regardless of velocity. Same IAS, same engine power
requirement. Look at some aircraft performance charts."

I'd always understood that power = thrust x velocity, hence the deduction
that it requires more power to go the same IAS at a higher alt. At the same
IAS the drag and hence the thrust is the same. Plug that into the equation
and you get the power required, which is more because TAS is higher at
altitude.

As for aircraft performance charts, they're for the most part in TAS, not
IAS.

However, the same author as the snippet above says:-

"The statement that power is drag time velocity is
incorrect."

Is it? I've seen that formula mentioned in almost every text on power that
I've seen.

Is there something I'm missing?

Not trying to be a PITA, just seeking clarification of something I was sure
was right. And I know that operationally TAS is much more important than IAS
except for, say, stall speed, best glide and the like. So it's a largely an
academic question, I realise. It was (sort of) started as a way of finding a
plain language non-mathematical explanation for the question "why does the
same IAS require more power at altitude?". I haven't found that plain
language explanation yet, but now I'm getting conflicting answers as to the
very definition of power.

Can someone clear it up?

TIA!