...informed me that unless I make my own prints in my own darkroom, the unique characteristics of the various films I've purchased will be made mute in the digital printing techniques...
...I'm actually shooting and developing my own black and white. But scanning for the moment...
So basically, you're saying that the photo clerk said that unless you're printing optically with an enlarger, that all B&W films are the same? No. This is hogwash.
Each film has its own certain "look," which you can then tweak in the developing and scanning processes, and the way you see it on your screen is how it will print. In fact, one could say that scanning technology is more sensitive to the particular inherent nuances in differing films than is optical technology. I've developed and scanned many different films, both native B&W and chromogenic, and can easily say that each has its own look, its own flavor. Some I love, some I don't.
The only thing I can contribute about BW400CN is that it has a very smooth, grainless look, almost like digital, and I'd expect XP2 to be similar. It's a beautiful film but you have the added hassle (and possibly shorter archival longevity) that C-41 developing brings.