OK. But you can't deny that Metallica guys are technically inferior musicians than guys in Maiden? Ulrich looks like an amateur compared to either Burr or McBrain and Hammett/Hetfield are much inferior guitar players than a Maiden guitar duo(Murray & Smith)? Serious argument could be made about bassists(who is better: Steve or Cliff). And vocally Dickinson puts Hetfield to shame. I think there is a general consesus that Iron Maiden is more talented than Metallica.
Let me preface this by saying that I'm only taking into account Metallica's output through the Black Album and Maiden's output through Fear of the Dark. While I have a couple of the "reunion era" Maiden albums, I haven't listened to them much.
You stuck a question mark at the end of the highlighted sentence, but it isn't phrased as a question. I certainly
can deny that and will do so.
In the late 80s and early 90s, Kirk Hammett was one of the most highly acclaimed guitar players in the world. He turned up in a number of articles/discussions alongside guys like Satriani and Vai. He was far more acclaimed than Murray and/or Smith.
Similarly, Hetfield has always been regarded as one of the best rhythm guitar players in metal. There's no analog to Hetfield in Metallica, but as mentioned above, Murray and Smith never got much run as technical players, so it's certainly the case that Hetfield was a more highly regarded rhythm player than Murray and/or Smith.
In terms of bass, Jason Newsted was never held in much regard. In part, that's because the bass was inaudible on AJFA, but there was nothing exceptional about his playing on either AJFA or the Black Album. Steve Harris, on the other hand, is one of the most highly regarded bass players in all of metal. The wildcard here is Cliff Burton. The bass on KEA, RTL and MOP is more audible than on AJFA or TBA, but it's still tough to hear on a lot of songs. It also generally doubles the rhythm guitar. However, Cliff is held in fairly high regard as a musician. In part, I think this is akin to Randy Rhoads and isn't entirely deserved -- especially because the discography is so sparse. At the end of the day, I think it would be hard not give Harris the win here.
That brings us to drums. I, for one, have never understood the whole "Lars is crap" mindset. Back in the day, I always thought he was pretty good. In retrospect, I'd say he's good but not great -- which is pretty much how I've always thought of Nicko McBrain. He's good, but he's nothing special and certainly not any sort of technical wizard. I'd call this one a tie (and I'm not factoring in Clive Burr as having added anything in terms of technical skill beyond what Nicko does).
Finally, vocals. I think Bruce is widely regarded as one of the best singers in the history of metal. James not so much, but his repertoire is far more diverse than Bruce's, and, as a "thrash" singer, he was excellent.
Overall, in terms of technical skill, I would say it's extremely close (at least for the era when both bands were most successful).