I believe much of the "softness" is ghosting and CA. Ghosting and chromatic aberrations are can really affect the final HDR image. The thing I like about HDR Pro is you have an opportunity to address the chromatic aberrations before the compilation is run. I used to ignore that page and just hit "Create HDR" but have found it makes a huge difference if you spend a minute or two adjusting the red/cyan and blue/yellow, for whatever reason, it also cuts down on what I call "the vibrational" look, for lack of a better term, that isn't really ghosting but gives it an aura effect. Actually, I think it's call "aura", now that I think about it.
At any rate, take a moment next time you're compiling your HDR and adjust the chromatic aberrations and I suspect you'll like the results.