I work on a lot of different bikes and other than the way the brifters feel due to shape, in my experience, Tiagra can shift just as crisply as my Dura-Ace groups. This is just shade-tree bike wrenching though. I'll bet new Tiagra feels better than Dura-Ace with year-old cables.
Don't get me wrong, I love my DA, but it's really just bling and grams. There are subtle engineering differences, but they're very subtle in feel too.
Maybe I'm just less sensitive to it due to the distractions of my screaming quad pain.