I found that I made better swings with longer irons like 7i thru 4i when I had a backweight in them. I don't know if it was the counterbalancing or just increasing the total static weight. The clubfitter I used for my last set felt it was just that I needed more weight and so adding the backweights brought the total weight of the longer irons closer to that of the shorter irons. We still MOI'd the set via headweight, but then I had ~ 10g backweight in the 7i and 15g in the 6 for example. On my own I played around with the backweights varying them with respect to shaft weight and grip weight.
I always felt like I struggled to lag the longer irons and the backweight seemed to help me from releasing early.....then again maybe just all in my head.