It's not the only way to judge a defender, for sure. But reliably turning the chances you get into outs is at least as important as range. Probably more. Getting to 15 extra balls per year is nice. But it doesn't outweigh booting 20 extra ground balls. Nor is range more important than knowing how to play the game, anticipate plays, and be in proper position. That's one reason why all the angst of the sabremetric community over Jeter was terribly misplaced. He didn't have range towards the end, but the Yankees kept playing him there because, in total, he was still a very good SS. He made the plays he got to, and almost never made the wrong play or was caught out of position.