The range of a fielder is very significant and varies greatly from the best to the worst. Of course, the pitcher matters and how many balls are hit towards the player or near enough to him, where it could be fielded. The difficulty of the play matters, both in how hard it was hit and how far away from the defender it was hit. Bad hops matter, too. We all try to measure that when watching some defenders make far -ranged plays, while others never seem to make any.
I guess you assume every fielder gets to the exact same type of plays, or the difference is so minimal, it hardly counts. To me, that is so wrong, it blows my mind someone can watch baseball and not see the variances in every game.
Yes, metrics are not perfect in measuring the variances or plays made and not made, and neither is the eye test, but I've never met a single baseball fan that use the eye test and say, the variances in range is so minimal, it should not be considered, let alone that a .995 Fldg % vs a .985 Flg%, which is the range of almost every defender in MLB is somehow more important. We are talking about a handful (maybe 2) of plays made out of a thousand, which is maybe 2-5 years worth of plays, is what you use to say player A is better than player B.