Yesterday I realized that I never taught my study group how to thrust. So naturally they were stepping in with bent arms, then they extended the arms, followed by an unbalanced lean of the body.

This is my fault, not theirs. When I instruct people with the rapier I always teach the principle of the point leading the hilt, which leads the arms, then the body, and finally the foot. But it never occurred to me that I needed to do the same with the longsword.

A lot of techniques fall apart without a proper thrust. For example, the absetzen often requires you to wind as you thrust. If you try to wind then thrust your defense will be weak and the thrust inaccurate. This is true for all straight-bladed weapons, be they one-handed or two.