The question of how "Purist" or "True Purist" SHOULD be defined might prove as fruitless on this formum as how "Folk" should be defined.

A more fruitful question is how it IS defined by people who use it. Don't expect any more consistency than you find with the word "folk."

I and my musical friends use "purist" to denote those who are trying to reproduce a sound.

For us it is rarely a pejorative term and we usually use the term good naturedly. We use it as more of a flag. The idea is to signal to the hearer that a certain approach to the music will be more welcome than others.

For us "purist" is not binary (Purist/Non-Purist) but analog (Purist on a scale of 1 to 10).

My impression is that for most of us in my circle of musical friends and acquaintances the sliding scale has tended to move towards the low end over the years.