While I understand where you're coming from on this with respect to high-end audio and other fields where eye-watering price tags are applied with poorly-defined reasons, this isn't the case here.
The espresso process is EXTREMELY finicky and highly sensitive to initial conditions. Recipes vary from bean to bean, machine to machine, and based on personal preference, but they all generally specify the same 3 things: the mass of coffee going in ("dose"), the mass of the resulting shot, and the time for the extraction to complete.
I typically am pulling shots with Madcap's Third Coast blend. In their shop they target an 18.5g dose yielding a 31g shot completed in 25 seconds (with no pre-infusion). The dependent variable here is the shot time. Anything +/- 4 or more seconds is dumped in the sink as completely undrinkable. The difference is not at all subtle - the shots are awful even to a novice palette.
The reason we have PIDs (and rotary pumps, heated group heads, calibrated tampers, doses measured to the 1/10th gram, etc) is to control every last variable that will impact this process. Every variable here can and will create wild swings in the resulting shot time, so we fix everything we can as accurately as we can to avoid dumping $1 worth of espresso down the drain. With everything else fixed, what we then control as the independent variable is the size of the grind.
This then is how espresso is tuned to land within the time given by your recipe. Grind finer (smaller particles), the process will take longer. Grind looser (larger particles), the process will run shorter. Anything more than 3 seconds one way or the other is another dollar bill down the drain. Very small changes in grind size can yield very large changes in the resulting extraction time. Every time you miss the mark, another dollar bill hits the sink.
As a result, grinder performance is probably the single most important piece of the espresso puzzle, and it's easy to quantify the difference.