So you are saying that
all it is is what some folks used to call a "slower" action? That is, the rod bends over more of its length? In so doing, it allows the rod to act as a spring to absorb force changes without snapping the line, is that it? Since spectra doesn't stretch, the rod needs to be slower?
In the diagram below, the "slow" action is also called parabolic because the curve resembles a parabola.
Funny how things go out of style and then back.