You're taking only INITIAL popularity and LASTING popularity issues. And no, popularity=/=impact and popularity=/=influence.
Did I say popularity = impact or did I say they were interdependent?
As I said previously, "Hallowed" was popular as a part of The Number of the Beast.
No. At least not only, as you suggested saying above.
Popularity can be judged in two ways. 1) An album or a single either makes the charts or it doesn't. It either racks up gold & platinum sales or it doesn't. 2) It is a concert favorite that remains in a band's playlist tour after tour after tour.
TNOTB, the album, debuted at number one on the UK album charts and it hit a respectable 33 on the US chart. That is where "initial popularity" and impact go hand-in-hand. If people are buying an album, that means that they are listening to it.
It eventually went platinum in the US and the UK. That is where "lasting popularity" will go hand-in-hand with influence. The more people listen to an album (or song) over time, the more influence it will have over time.
(EDIT) The studio version of "Hallowed" was not released as a single in 1982. That is why I say that it was popular as a part of TNOTB. But I can say the same thing about "Invaders" and "Gangland". All three are kick@ss "metal" songs, but it was "Run to the Hills" that hit number 7 on the UK singles chart, not "Hallowed".
Now I have seen Maiden in concert a few times. Every time folks in the crowd were calling for "Hallowed" and they always played it somewhere in their set. But they also played "Run" and "Number" as well.