I dont know about everyone else but I dont get any more power from pushing off the backfoot when using the jabbing hand. Im left handed and find and teach people to drive upwards on the leading foot for power in the jab. Theres a sequence that needs to be followed to make the most on the momentum and not waste the energy that could go in to a simple jab.

I broke my right hand by punching a wall in temper in my last season and couldnt use it even lightly for months. So I only used my left for months on the bags and the pads. My left got as good as I think it could get. I learnt how to drive properly to get force through it and it was sharp and had a loud clap sound sound when it landed on the pads or bag because the distance was right. I know not everyone is a big puncher but in my gym my jab was harder in the end than some of the other lads rights. My major problem was arm length. Holding a tape measure between the top of my right bicep where it meets the pectoral muscle down to the wrist is only 19" and im 5,9" which I think is disproportinate arm length?

If someone was taught how to use the jab so it actually hurt an opponent they wouldnt bother using it to flick out with.