The results of your experiment seem to indicate that a shorter shaft made no difference for you, in either distance or shot dispersion. I don't know why you then extrapolate at the end that it will work better for other golfers. I would assume some people do get higher clubhead speed out of the longer shaft, it is just a matter of whether the likely increase in shot dispersion is worth it. If your normal dispersion is only 10-15 yards, going to 15-20 yards is probably not a big deal if the courses you play have wide fairways, and even 3 or 4 extra yards would be worth it.
The fairways on my home course pinch in to <25 yards in places, and there are only a few holes where you have more than 35 yards - and more than 5 yards off the fairway is in almost all cases in the trees. I can play 10 shots worse on a bad driving day because of how costly this can be. Since I only beat 50% fairways hit on that course on a good day, taking any hit on shot dispersion isn't worth it for me, even if I could somehow gain 10 yards with a longer shaft.
It would be interesting to measure this for myself like you did, I admit I've never tested the assumptions that 1) I'd hit a driver with a long shaft further and 2) I'd hit a driver with a long shaft less accurately. Perhaps like you, it makes no difference for me. It makes sense that a longer shaft would increase clubhead speed, but I'd have to swing it a bit flatter which may cause me to lose some mechanical advantage during my swing. I really don't know for sure.
Its not necessarily easy to test this 'objectively' since you never seem to swing equipment you're not familiar with quite as well. I borrowed someone else's driver a couple of times a few weeks ago during my visit to Sand Hills and the 5th Major, and both times I hit a drive that I felt like I absolutely nutted, but it went the same distance as a heel hit with my driver. Both times I was expecting it to be 20 to 30 yards further than it was based on how it felt.