tough question
What do you think makes the difference? Joint, shaft taper, tip combination of things?
That is a simple little question that is extremely tough to answer. When one thing is way out of the range of other things it has a large effect. Otherwise everything up to and including the bumper has an effect. I need a bit unusual bumper for one of my cues. Keep meaning to order one but I don't need anything else so I haven't gotten around to it. I'm not big on slamming cues down on the floor and the cue missing a bumper is pretty old and ratty so I don't particularly need the bumper for protection however it and a cue I "borrow" a bumper from when using that one hit too differently with and without a bumper to shoot without one.
The general theory is the closer to the impact point with the cue ball the more something affects the hit. Tip, the oft overlooked ferrule, shaft, joint and collars, forearm, handle and wrap, and the bumper or lack of bumper. No surprise that I agree with Sean, the bumper or limbsaver can certainly change the hit. Tips obviously can, as can the joint. Interestingly almost invisible and extremely difficult to feel changes in the taper of a shaft can have a huge effect on the hit. The original properties of the wood or laminates of the shaft often have a huge amount to do with hit. As I think most will agree, two seemingly identical shafts with the same tips, ferrules, and joints can have vastly different hits.
I really think that when we play with the shafts with many laminations that we are playing more with the splices than the wood, a synthetic shaft. The wood provides the bulk and the contact surface for our bridge but the splices provide the support structure. Note this is opinion, I have never tried to prove this by carefully controlled testing. Tough to do since one plain wood shaft can vary so much from the next. The best wooden shafts, no laminates, have been reported to have 3% or less variance in radial consistency. I doubt many laminates including the pie slice style test much better than that or that a difference that small affects many shots or the feel of a cue in any way.
I have been wanting to build a cue with just enough collar material on it to protect the wood at the joint in order to test wood to wood hit and how other materials transfer feel. Think collars that are only maybe a tenth of an inch thick in each dimension, more rings than collars. One more project it seems I will never get around to.
A pad or very short ferrule works just fine to protect a shaft too so experiements with ferrules could yield interesting results. High speed photography shows that some ferrules bend and give far more than I would ever have imagined. Ferrules need far more consideration than we usually give them.
You asked a simple question, believe it or not this is the short version of my answer!
Hu