I don't disagree with that at all; but if you're going to claim something is "objective" it ought to be measurable.
"Back In Black" is a better album than "For Those About To Rock"...
... based on album sales and number of songs in the setlist from that point forward? OBJECTIVE.
... because one person, in this case, me, listens to BiB more often? OBJECTIVE. (Someone can, if they wanted, count the number of times I've listened to it)
... because I like it better? SUBJECTIVE.
You'll note that the best critics (in the classic sense of the word) will almost NEVER base their conclusions on "I like it!" but will almost always give a context to any conclusion they draw.