Joe, you seem to be saying that lower deflection is equivalent to "better." I'd call this a personal preference you hold rather than a fact applicable universally. Some players, for legitimate reasons, prefer a shaft with higher deflection than your Z2. To them, lower deflection would not be better.
Let’s say you have a car that tends to pull left or right as you accelerate into a turn. The more you accelerate the more it pulls. On soft turns it can get goofy as it doesn’t always grab like it should.
If you grew up with that car you would be used to it and might even prefer it over a car with power assisted steering. I guess that could be considered a preference.
However, when engineers find that several of their cars are acting in this hard to steer way they re-engineer the car so it responds better at slow and at faster speeds. The “new” engineering is a “better” driving system. None-the-less many people grew up with the old difficult to steer cars and still prefer them to the newer equipment. For the older people it seems the old way is better and they have to re-learn to steer a car that doesn’t pull.
So in a sense you are right, it is a preference. However, it has been unequivocally demonstrated that cue sticks made with lighter “front ends” have better playing characteristics. That is not opinion. That is fact. So the preference is for a type of stick that really doesn’t work as well. It is something like going from driving a tractor to a car with power steering. The new car requires a much lighter touch and this has to be learned.
The analogy between cars and cue sticks breaks down when it comes to the subtle differences in cue sticks. The cue stick improvement is not immediately apparent to the newer player who has to test the differences between sticks. Heck some people are not even aware of what happens during deflection. With the newer sticks one does quickly learn that it is possible (and easier) to stay closer to center ball for the same effect.
Older (especially good) players have learned that deflection is part of their game and have mastered its effects so they don’t “need” the new fangled equipment.
For me it simply makes sense to reduce (not eliminate) whatever error inducing effects I can remove. I guess this could be considered a preference. The older player tells me to learn to deal with it like he did.
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By older player I mean older in experience not older in years.