But for me the question is never "Who is the finest pianoist?" but rather "Which pianoist is least inaccurate?" In a perfect world every performance would be perfect and all pianoists equal. Whoever first introduced the concept of "interpretation" has a lot to answer for. In reality the interest lies always in how the composer's intentions emerge DESPITE the pianoist.
So "pianoist" is the latest Grewist invention, I see? Anyway, no one ever "introduced" the idea of interpretation but your "perfect world" is not one that makes sense to the composer who knows as well as anyone that there's never a single "right" way of performing anything; composers revise their ideas both during and after writing works and they are amenable to different ways of going about them (within reason, of course) just as their ideas about them change over time. Speaking personally, I've occasionally found a performer who really understands well what I'm up to who suggests the odd minor amendment in order to make it sound even more like what I wnat that what I'd written does - and that is always a most gratifying experience.
Decades ago I had the privilege of attending a Scryabine recital in Hong Kong by Shura Cherkassky which has remained in the memory; several late sonatas. Afterwards I was able to discuss their wonders with the local population.
Cherkassky's performances were almost always memorable; at his very best, they were models of hyper-control and technical near-perfection but at the same time brimming with so rare an electrifying spontaneity that the listener could be forgiven for thinking that he'd just written all the music himself; I even remember him turning out a Liszt Second Hungarian Rhapsody that simply danced its way off the concert platform and sounded as though the ink was still wet on the page and gave the impression that one had never previousy heard the piece, which is quite an achievement in itself. He seemed to be a rather strange man who had remarkably little in his life besides the piano, but there's no doubt in my mind that he was one of the finest pianists of his generation.