I feel like a player's choice of X or Y comes from how much they balance the use of the Z button and C-Stick.
X-jumpers press their button with their thumb and tend to rest their index finger on Z. The upper lip of the trigger for the R button limits their ability to use their index finger to press it, so they prefer to use L to shield since the left index finger is otherwise completely unoccupied. Some X-jumpers also use their middle finger to cover R for doing a WDOoS, but those who don't utilize this option simply keep this finger gripping the controller by mirroring how their left hand grips it.
Y-jumpers press their button with their thumb (unless they utilize the "claw" position, in which case none of what I'm saying applies) and tend to rest their index finger on R. This limits their ability to simultaneously use both the C-Stick and the Z button without putting lots of strain on their fingers, as they would either need to stretch really far back with their thumb to use the C-Stick or to keep their index finger bent sharply at both of its upper joints for the entire time that they use the controller. They can choose to forgo the use of one in order to comfortably use the other, but this is not practical for obvious reasons. Many Y-jumpers are forced to use Z with the midsection of their index finger rather than with the pad of it as a result, which makes the Z button less responsive. Attempting to use the pad of the index finger while trying to use the pad of the thumb for the C-Stick leaves the Y button out of reach. At this point it would make a lot more sense to use X to jump since it is actually still within reach if the Z button and C-stick are used frequently.
A surprising amount of players don't touch the C-Stick at all. Many others don't use the Z button either, preferring to use R + A to grab or use custom controls to assign the grab function to one of their unused jump buttons. It's a strange world out there.
To put this in perspective, I used to sexually identify as a Y-jumper. After about a year or so, I realized how much my hands hurt after trying to incorporate the Z button into my game. I play G&W, so this was a huge problem for me whenever I tried to use my really awesome DACUS (which I'm pretty sure is the only time the Z button and C-Stick would ever be used in conjunction). Many people have told me that making the switch to another jump button after using one particular button for a really long time is close to impossible, but ever since I made the switch to X I suddenly felt very comfortable playing my character. The new position immediately felt natural and my ability to play my character improved as a result. The only problem with this that I've had to deal with so far was making the transition from using both triggers to just using the left one. I've had to set my R button to "None" to prevent no-reason airdodges and to encourage myself to keep my index finger on the Z button. I miss my L-Cancels pretty much all of the time now since I'm still adjusting, but at least I can feel good about it since DACUS and JC grabs are amazing.