I can change the voicing of my entire system simply by changing the rectifier in the power supply to my phono stage. The biggest improvement to my current main system, the core of which started in 2006, was probably the change in cartridge, but everything else was up to snuff. I don’t know how to assign priorities or percentages simply because there are synergies and I guess I subscribe to a weakest link approach.
I also have no holistic view about system building beyond knowing what I hear, first hand. There are some known synergies, but a lot of factors go into sorting the system set up in the room to maximize its potential. In this sense, even using the same gear, I think every system almost becomes sui generis.
Not dismissing the question posed, since I responded but I suspect you’ll find that some folks will be able to get great music out of a well set up vinyl front end with a modestly priced cartridge.
So, my response should not be taken as a "rule" to apply to others, but rather, where I got the biggest uptick, once everything else was primed for it. Too many variables for me to wrap my brain around, perhaps.