Great post/discussion topic everyone! As a pianist, I have to agree with the premise that while the typical stereo sampled piano instrument (low notes to the left, high notes to the right) is interesting and can be useful in the right situation, it's not what I would consider inherently realistic, and in many cases it comes with such a wide stereo field that it's not a good fit in the mix. And simply panning the stereo signal, which acts like a standard balance control, is only going to accentuate either the high or low notes, not what you typically want to do. But there are a couple of other options you can experiment with. You can split the stereo signal into 2 separate tracks for the Left & Right signal, where you can then play with the pan each of those tracks (to do this, create another track and option-drag the original onto it to create a copy, then click-hold the stereo symbol on the channel strip and select Left for one track, and Right for the other). Also, Logic comes with a processing plug-in tool (they call it the Directional Mixer) which lets you narrow (and expand) the stereo field, in this case you can make the stereo signal "less Mono", all the way down to a true Mono signal.
Hope these give you some ways to do what you want. Have fun!