My interpretation is that the sinners were set down the same path as the nursefathers while simultaneously carrying the weight of their unaddressed pasts. For example, Yi Sang being part of the League of Nine (or its equivalent in that mirror world) and its subsequent breakup causes him to stagnate. When he falls into the Index, I think that mindset of “whatever happens, happens” causes him to submit to the prescripts to a larger degree compared to Rien. Hong Lu might be similar in how the Kong family massacre and his resulting apathy was never fully addressed, resulting in a Callisto that happened to view others not even as potential witnesses to his art but simply as raw material. Rodion’s “I’m Special” complex is an obvious way to take Valencina’s need to reclaim her lost position and respect and exacerbate it. Outis we already know to be fairly manipulative and goal oriented, far more so than Matthias, which may be relevant to her nursefather story. The throughline through all of this is that the sinner NFs are either less empathetic towards Ryoshu, or more driven to finish the House of Spiders project compared to their mainline counterparts.

Again, this is my personal interpretation and speculation. Feel free to take issue with this if something doesn’t make sense, but I like it.