No way to know why you’re experiencing the shorter distance. Are the clubs the same length? Are the lofts the same? Standard stock lofts of each are similar. Both of these elements have more to do with distance than anything in shaft. If they are the same, then might as well try another shaft to see what happens.
Without seeing you hit shots with each and without being able measure the specs to see if there is anything that is noticeably difference that could cause the distance difference, I can’t really pin point what the issue might be.
Britt Lindsey
If possible get on a simulator with both 7 irons and compare data. Those Maltby shafts are quite a bit lighter. If anything you should be gaining a bit of clubhead speed with the TS3 build. Something doesn’t seem right. Possible that the Pro series isn’t a good fit for you. Too much spin. Or the KBS are not giving you enough spin. Maybe your club head speed is down with the TS3??? Either way the data would show why or where you are losing distance.