The internet wisdom premise is...... if you changed from iron to aluminum heads, all else being equal, you’d lose power...... because the aluminum absorbed some power away.
And...... you’d have to up the CR for the aluminum headed combo to be equal to the iron head combo.

The test in the link I posted did what I feel is a pretty thorough test of that in a very “man on the street” type of build.
The difference in power was with the margin of repeatability for the dyno.

That’s using heads that are as close as possible to being the same, other than the material they’re made from.

In the case of what most people here are doing......if they’re going from iron to aluminum....... you’re almost never comparing equal heads.
In most cases, you’re replacing iron heads with better flowing aluminum heads(otherwise.....why are you changing the heads?).

It’s going to pretty hard to come up with some sort of “high performance” build combo where the better flowing aluminum heads get out powered by old iron heads.