1) 2K has to do a better job out of the box as far as getting things close to realistic for an average person of each skill level.
2) It will never be right for everyone out of the box because everyones skill is different.
The problem is that because they do such a bad job on #1, sliders that should be used for #2 (minor tweaking) instead of major re-programming.
On a high level, say All Star or Legend, why should anyone have to change the speed of fielders or baserunners? This speed if realistic to begin with, should never have to be tweaked. But because of other factors (hit variation, scaling of the ball parks, etc.) it has to be fixed. In reality, it should be right and any changes should only have to be to a select group of players that were given the wrong speed rating.
The same goes with errors, a player who makes 20 errors a season, should be programmed so that on average, he makes about 15-25 errors a season or about one error every 8 or so games. It shouldn't be that everyone makes a ton of errors or nobody makes an error. A good fielder should be noticabley better than a bad one.