I have both, and use the 24mm 1.4 when I can - because 1.4 is much better than 2.8You're correct, and in my case, I never had clients who appreciated that type of shot, so I never went for it. I've seen some amazing bridal shots and portraits with 12 and 14mm lenses, so it's definitely possible if used correctly and I'm sure you've taken some great ones
It is true that shooting people at 16mm is a challenge. But, if you keep them dead center, generally most of the distortion is avoided. If you do it right, you can actually make some quite impressive photos where you essentially isolate a mostly-undistorted subject via distorton (instead of say bokeh).
Generally I use the 16-35 for parts of events where 24 won't be wide enough, or for the ultimate in environmental portraiture. Is having 16-23mm absolutely 100% necessary? Probably not, but then again those unique shots is what can make your work stand out.
One very cool thing you can do with shift lenses is shift to the side and then frame a person on the opposite side to the shift, doing this you can put a person on the extreme edge of a 17mm shot with no distortion.