In my experience, IR cannot always be used as "gold standard" for LiPo health. Though we can say if one cell is twice the IR of the other cells, that cell is probably bad. Additionally if one pack has 1/3 the IR of different pack, then its likely to have a higher C rating and perform better.
But I've had some cells which were clearly under performing as evidenced by a significant voltage drop under load. But these same cells had IR numbers that were close to the other cells in the pack.
While IR can be used as an indicator, a much better method would be to use the PL8s regen discharge into a Pb battery and log all the cell's ability to hold voltage under load. The FMA CCS makes very easy work of this.