I see! That's a fair observation - I didn't think about that, really!
I may be simplifying the things a bit too much, but when it comes to Maiden, I don't think (or want, anyway) they're attempting to surpass any of their past works per se, just to focus on the task at hand and make a best record possible in the (then) current situation without too much of a comparison with their previous ones. I can see where you're coming from, but I think the gap between Maiden albums is more of a result of their somewhat loosened schedule, rather than artistic ambition. Looking at the way they put songs together and record nowadays, I don't think there's much of attempt at holding any specific standards on conscious efforts at keeping up with the standard set by this or that record; for better or worse, they're "just winging it" on the go.
Granted, as you mentioned, it would be quite healthy to just maintain that routine; that might have lead into some missteps over the years, but sometimes those are the ones that make your next work so much better. Maiden has been releasing one mammoth record in 4-6 years since 2006 and while I don't think the gaps between the albums are specifically an ambition-related issue, they might set some (whether acknowledged and conscious or not) standardizations for the next record... so maybe there's bit of a that behind every record since AMOLAD getting bigger and bigger, whether that's a good thing or not. Senjutsu is obviously a little bit shorter than TBOS in terms on runtime, but looking at it's "structure" it might very well be their most "sonically massive" record since Dance of Death.
Anyway, you made a very good point!