When Gorden Moore wrote his first paper on things doubling every fixed time period it was on the lowest cost transistors back in 1965 but the term Moore's Law didn't come into use until the mid 70s by which time he had written a number of other papers pointing out a number of other doublings including feature size. In the old days these all doubled in lockstep so the original coinage of the term didn't really distinguish economics from minimal feature size.

So there's really no legitimate way to insist that Moore's law has to refer to the lowest cost number of transistors. It actually wasn't that by coinage and it certainly isn't that by common usage. I've even got a copy of a memo by Moore in my 6.175 lecture notes endorsing a broader conception of Moore's law.