I wouldn't really say the Nier raids are longer (aside from Paradigm's Breech, mostly because of drawn-out cutscenes), so much as they show you how much of the party is slacking off. Power creep and inflated item levels have made Crystal Tower such a joke that half of the bosses in the first two don't even get to do most of their mechanics anymore. A group that's on point in Copied Factory can skip plenty; I've seen parties that burned down the second boss before the floors made a complete rotation, or killed 9S before he could take his second bombing run, or Engels before he tried to clap. But a lot of people in Duty Finder slack off, so it's more noticeable.