First, the difference in a 1020 carbon steel and a 1035 carbon steel from a harness standpoint is minimal and not noticeable. You can’t go by just those numbers either as there are other processes involved that determine the overall hardness. They are very similar.
With regards to the hosel length, it would have nothing to do with the stiffness of the shaft. The bore depth might, as the bottom of the bore to the heel dimension, if shorter, would increase stiffness. If the bottom of the bore to heel is longer, the shaft could play or feel softer. this assumes the shafts were trimmed exactly the same if you are comparing. Also, I am assuming the head weights are the same. If there is a variance in the head weights, it could make a difference, although I would suspect any difference would be small.
I have not measured the Bridgestone J40 DPC iron so I have no idea how stable or forgiving it may be compared to the TE. I know the TE is a Super Game Improvement category players cavity and has been a best seller and performer for us for years. A more stable, more solid feeling strike, at least to me, feels “softer” than a strike on a head that is less stable and less forgiving. Of course if they are both struck on the center of the face it doesn’t matter. Just throwing that out there as a possible reason why they feel a little different.