Phono preamp or SUT for low output moving coil

Actually, you can change the load resistor in any MM stage to whatever value you prefer, if you can identify it and can solder.

I wouldn’t go so far as to say "any" since the input impedance may be determined by more than a single resistor, but it is certainly the most common way. Hopefully whoever is in there replacing  resistors knows enough to determine what is needed.

The caveat with going too far is that increasing the input impedance also increases the amount of noise that gets in, so there is a practical limit

I agree with most of what has been discussed, but would like to point out that there is no conflict between the use of an SUT and choosing a phono stage that has an accurate RIAA curve.  I guarantee that the the use of the two together can be serendipitous.

The question or the argument is how accurate is accurate enough?

Before this turns into another one of those senseless debate….the answer ultimately depends on what “accuracy” means to an individual and how it aligns with their listening priorities.

You will probably not be surprised by my answer.  Measurements get us to a certain point, they do not absolve us of the responsibility, or perhaps even better, the necessity to listen and decide what sounds we prefer.  It is usually the case, but not always, that someone who knows how to listen will prefer equipment that both measures well and reproduces accurately.  Of course taste comes into it too, hence looking at audio broadly there are horns, dipoles (electrostatic and planar) tubes, various solid state devices, Class A, AB, D, MM, MC, digital and analog this and that and all manner of other equipment variables.  All technologies can measure well, all have distinct sonic signatures, and of course all have their adherents.  So it is not possible for me to answer your question in a definitive manner.  Subjectively though, to your question how accurate is accurate enough? The answer is accurate enough to please the principle listening audience.