I mean ... for and given work of any given artist there exist some critics that don't (or won't) understand their work.
The guys in Metalica are, I think, quite legitimately the Lennon-McCartney of their genre (something I think the "Black Album" is kind of riffing on). But for a long time, I really didn't get it at all. I still don't much care for most of their work, with a few significant exceptions, but I do understand that this is really good music within the context of the genre (and a genre which they helped significantly to bring into existence).
Ambient piano, like thrash metal, as a genre is ... something I could mostly take or leave.
Sometimes a really good ambient composer will tiptoe into the minimalist edges of the neo-classical, which completely changes my reception.
But assuming that we're taking the ambient piano genre as ambient piano music quo ambient piano music (ie. and not trying to make it neo-classical, much less holding it up to Lizt), what would the work of the "Lennon-McCartney of the ambient piano genre" even look like?
I have no idea. Because I just don't care enough about the genre to even wonder too vigorously.
But suppose a given composer genuinely is the "Lennon-McCartney of the of the ambient piano genre" ... it would make perfect sense, I feel, for them to rail against critics that make Lizt or Beethoven or Metallica or Lennon-McCartney comparisons. In much the same way that compared to my favourite Beatles records, Oh My God Metalica sucks!
So for a critic too project Metalica onto the Sgt Pepper ideal and make evaluations would be simply to misunderstand the genre.
So I don't need to like the music of an ambient piano composer very much to be sympathetic with pushing back on critics who don't understand their work. In fact is seem entirely inevitable.