I think in general people give too much credit to the shifters for the "smoothness" of the shifting. The shifter just pulls and releases cable. How well the cables are installed and routed, as well as the adjustment of the deraillers makes far more difference. The front shifting is also going to be greatly affected by the chainrings, the profiling of the teeth, the ramps and pins, etc...
I would agree with this.
I have Tiagra on both my Aurora and my Bianchi.. they both feel so completely different, I wouldn't even think they were both Tiagra if I didn't know. The Aurora feels rough and seems to take more effort while the Via Nirone just feels smooth and easy. I tested a carbon bike with 105 when I got my Bianchi and I didn't notice much difference.