Irons are a piece of metal with small variations on where the centre of gravity is placed and stability when hitting outside centre. The distance is basically depending on the loft and not on technology. The KE4 V are easy to hit.
You should look to other parameters to find the reason for your loss of distance. For instance lie, shaft length, flex, swingweight.
Also be sure that you hit the ball cleanly. You can measure the clubhead speed of new and old irons and compare. If similar, it is the way you contact the ball that is the reason for loss of distance.
Also compare ball flight. High, low, weak, strong, spinning ball, lot of roll…
