What I always want to know in these polls is the age breakdown of who votes for what. We're ranking an album that came out well before a lot of people here were born and judging it by modern standards. In terms of who was better musically that's alright, but I think you also have to take into account, at least somewhat, the effect they had on the musical landscape. BiB was a sound we hadn't really heard before. GnR was derivative.
In general, I think you are right, if we are trying to ascertain which album is better in a more "objective" way. But isn't that basically an impossible exercise anyway? Plus, the idea of contextualizing the historical importance of a record is especially relevant if we are comparing something that came out, say, 5 vs. 40 years ago. But, even sharing your view that BiB was less derivative and had more of an effect on the musical landscape than Appetite, we are still talking about two albums that came out 41 and 34 years ago, respectively.
Musically speaking, GnR were definitely taking plenty of cues from Aerosmith and a harder-rocking version of the Stones, but they were very much their own thing, in many ways, already on Appetite. There were certain elements in the songs that were borderline metal and, as was mentioned before, some of the intricacies in the arrangements and guitars' interplay between Izzy and Slash were way beyond what the glam/street metal bands were doing at the time (IMO). I first heard Appetite in 1989, and I was 12 at the time. I discovered AC/DC a little later. BiB is a great, iconic album. I find Appetite nearly as iconic and, musically, I just like it better.
But, at the end of the day, it's a just lot of fun to think about these comparisons - and it's a good excuse to revisit timeless classics (although I take it you don't necessarily share this view when it comes to Appetite
)