I appreciate the discussion and hope you appreciate that I am simply attempting to reconcile my subjective observations with objective measured facts.
One of my huge disappointments was the JL Audio E112 sealed sub.
Looking at the incredible build of the driver and knowing it was sealed, I really expected it to handily beat my Rythmik (did not yet have the XS15se). It sounded like a ported sub to me!
But maybe I can rule out GD as being the issue because the GD chart for the E112 is pretty good:
The impulse response is not so good:
So, right now, I am thinking it is either:
1) frequency response (after room gain) or Impulse response.
2) Q, but it seems like the end effect of this would show in the measurements.
3) Something measured that I have overlooked
4) Something which the Data-bass measurements do not reveal.