It's a proverb, meaning it's not wise to criticize a small flaw in one thing while (in this case) praising something else that has a far worse version of the same flaw.
To be clear, I have no problem with you preferring BNW over AMOLAD, but it just seems weird to make that specific point of comparison.
Anyway, I think I now understand that your position is that repetition like that is not a flaw as such, only a flaw when the repeated melody is not good? I would disagree with that, and would rate the repetition as a flaw even when it's a repeated part that I really like, such as the second chorus to For the Greater Good of God. But if I've gotten your view right this time, I understand.
Re: Book of Souls and production, honestly, I don't like the production on any of the reunion albums. BNW is fine, I suppose, but the other four are rather poorly done. Ideally, Steve would back off production, bring in someone other than Shirley, and let a studio album actually sound good for the first time since 1992, but I doubt will ever happen.