What matters more, the butt of the cue or the shaft of the cue? It’s definitely the shaft of the cue. It’s true that the butt has some minor technology used in it’s construction but it’s nowhere near as advanced as the shaft.
Manufacturers spend a lot of time perfecting their pool cue shafts and they pride themselves on how much amazing technology goes into their constructions. Their pride is well placed because, frankly, it’s kind of amazing how scientific they get when creating these shafts.
A quality, high-performance shaft will be laminated, have a hollowed out top, etc. These will all be beneficial in helping to create a low deflection shaft. Lower deflection means more accuracy which means more repeatable shots when you’re actually playing a game.
So, if you’re stuck and trying to decide how best to improve your cue’s performance, I’d recommend that you start with upgrading the shaft. This will be the most noticeable improvement and you’ll absolutely get better play out of the cue.