No, because they don’t mean “retain heat” in the same way you do. The goal is so that when you put something cold on a hot pan, it doesn’t immediately cool down, but rather that the surface stays hot and keeps searing your food. Thus, if the pan is not very conductive, the surface will cool down, and the heat “retained” in the interior of the pan will not be useful. In other words, the goal is to retain the hot surface, not the heat in general.
Aluminum actually has about twice the heat capacity (separate from conductivity) as cast iron.
I haven’t seen an aluminum pan that was even half as heavy as a typical cast iron skillet is, though.