It's funny I've seen this a lot before but I really feel TFF is one of the more unique albums of the reunion era. It's true that it feels like a straight continuation of AMOLAD, more than any other pair of Maiden albums outside maybe SIT to SSOASS or the first two albums, but despite nearly every song being a rehash of the framework of a previous song (usually on AMOLAD), I think they innovated a bit within those frameworks. The backwards guitar solo on Man Who Would Be King is a good example, or just having a proggy Murray epic in general is kinda unusual. Both Starblind and Isle of Avalon (the latter especially) feel unlike anything Maiden had done before, with Avalon in particular being the closest the band gets to approaching straight up progressive rock. Obviously Satellite 15 is kind of its own thing. Even songs like El Dorado and The Alchemist feel like the band recapturing their 80s energy in a way that we hadn't really heard during the reunion era up until that point.
But yes, I agree with the overall sentiment that Maiden is a formulaic band, especially in the reunion era, but I think that works for them. There are some bands that I like to see change things up a lot, but I like that Maiden stick with what works for them. It makes their discography much more consistent than, say, Judas Priest.
I will say that the biggest factor over the years that has contributed to distinguishing Maiden albums from each other is the production, especially in the 80s when each Birch album seemed to have its own sonic identity. Obviously that is less the case now, but I don't think it's a coincidence that the better produced albums (SIT, SSOASS, Brave New World, AMOLAD, Powerslave) tend to be rated higher than the ones that don't sound as good (Dance of Death, X Factor, maybe the last two).