This is an interesting read although I think there are some wrong conclusions being drawn from the OP and some comments. Ever since hearing Senjutsu I've had the strong suspicion that somewhere in the process (anytime between finishing the album initially and it sitting in the vault) some songs may have been remixed. Writing On the Wall, Days of Future Past, and even Stratego are among the best Maiden has sounded in the Shirley era. Meanwhile the title track and Lost in a Lost world sound almost as bad as The X Factor. Either that or Adrian has gotten more of a say in production choices on the last two albums. I've also noticed that Adrian significantly changed his writing style on the last two albums. No more big proggy epics and instead we've gotten more immediate up tempo rockers in the vein of the 80s. Not sure if that's a response to production as well but I could certainly see him trying to write songs that better fit Maiden's production style rather than more prog rock epics in the vein of Starblind that are going to sound rough in a Maiden studio situation.
Where I disagree with some of the conclusions drawn from Adrian's comments is the degree to which he wants Maiden to go more produced. I don't think Kevin Shirley is a hack and I don't think Adrian believes that either, especially considering Kevin Shirley mixed the Smith/Kotzen album. And to that end, if you listen to Adrian's recent solo projects (of which admittedly there aren't many), they are not the most polished products out there either. I hear more reverbs on the guitar and more vocal polish primarily, but it's not a far cry from the way Maiden's albums sound. Additionally Adrian clearly sees Brave New World and The Book of Souls as high water marks for the band sonically even though they're still in the same production style. In a lot of ways I think it could be as simple as Adrian just not liking the way his guitars and Bruce sounded on Final Frontier. After all, Kevin Shirley did say he was "95% happy" and the sticking point seems to be largely around the amount of reverb. It might not be as severe as how the fans feel.
People in here are talking about Andy Sneap sounding albums even though the new Priest albums are produced to extremes that Maiden never went to even in their most produced 80s albums. The layers of guitars, the drums, vocal parts that could never be pulled off live, that's never how Maiden made their albums. And even in the 80s Priest was more produced than Maiden.