I am not making any reference to ease (or cost) of replacement and and just acknowledging that a PU is an important part of resultant tone. I've swapped a few (awaiting a delivery right now in fact) but I don't treat them as a consumable - just a way of sculpting the tone.How can PU be important when they are so easily replaced. Your fundamental tone starts with the instrument and then you get PUs that are sutable for the gain levels that you use. They are important but they are more like the set of tyres you put on your Ferrari .
Ever owned a guitar that just didn't sustain a note in certain areas of the neck? Very far from negligible.
Some people care more than others about tone and that's up to them but it doesn't mean the effect is less. Gear you play through and the player are a huge part of whether this comes to the fore or not. A really great player with a great amp is going to push right up to the potential of the rig and you WILL hear it.