There are notable differences. Example: take the song No More Lies. The chorus is just repeating the line over, always in the same manner. Now take The Evil That Men Do. The chorus is the same line over too, but every repitition is slightly different in melody and phrasing. The key here is detail. It is what makes the difference between an okay song and a great one. Newer Maiden material has a significant lack of detail when compared to the classic stuff. There aren't many songs in their old catalogue with repeated chorus lines, and those that do have more variation.
Song lengths are part of the arrangement, and that's detail too. In songwriting, the arrangement often takes longest. Same for me. Writing he basic song parts is usually quick. Finding the proper arrangement can take weeks and monhs per song, at least if you want to stray away from the ever formulaic verse-chorus-verse structure and also want to avoid sounding random.
Writing longer songs is very difficult as arrangement becomes way more crucial than with 4 minute songs. My band writes songs with average song lengths of 11 minutes, thus we spend months on arrangement alone.
Admittedly, blaming this on their writing modus is speculation on my part. Could have other reasons too. But Maiden clearly take less attention to detail and arrangement than in the past, which is detrimental as their songs grow longer. I think they could avoid this with simply taking more time with the arrangements. Especially since they have MUCH more time between albums than in the past, and a budget that easily allows it.
Other bands can't afford to work differently, Maiden could.