for the life of me i can't seem to find this youtube video that i saw awhile back. it was really good. basically the guy hits a shot to demonstrate deflection then puts a vice grip on the end of the shaft, clamps it down then deflects the ball like 3 diamonds, illustrating shaft-end mass contributing to deflection. I think it also demonstrating clamping vice grip to joint area and having no noticeable impact. it was cool and informative video.
As an experiment for yourself, try taping some lead or something heavy to the end of your cue and notice the change in deflection regardless of whether or not its an LD shaft.
Tip contact time does not vary noticeably even based on tip hardness let alone shaft flex. For your statement to be true, you would have to be assuming that a high deflection shaft would be flexing so much that the cue ball doesn't leave the tip until significantly later than normal because of this flex.
The cue ball simply doesn't weigh enough to prompt this logic. Maybe if it were a medicine ball then this would matter.
Since the thread is calling out dr. dave, i think it would be really cool to glue a tip onto a fishing rod and measure tip contact time with the cue ball using something that would flex like a mofo. I would love to see that result. I would do it, but i don't have that super awesome camera equipment.