I think fit and finish are part of the equation (okay, finish more for aesthetics), but one aspect which may be considered part of the precision is tolerance and I find this is not on par with the 418. Tolerance is not tight enough to ensure things don't shift around, and I found on my chassis, the split suspension blocks have to be realigned very carefully if disturbed (say when adding/taking out shims), otherwise you can end up with wild problems (like unequal toe). This is not okay in my view. Tamiya now provide a different design split block for the 419, (like the Yokomo one) so I guess I'm not the only one who noticed the problem. Even the single blocks can move around a bit enough to require careful tightening down for a play free suspension assembly.
There are other areas that need attention in my view, such as the bulkheads, the shock towers, the servo and motor mounts. Locating keys are useless if they allow that much movement. Not to mention adding to the cost of manufacture for no benefit. These need to have tighter tolerances (probably more expensive), or could use a better design with inserted steel pins captured by (grub)screws (hopefully cheaper if they would cleverly use screws already there) or interference captured steel pins in one of the mating parts.
The Avid from Robitronic comes to mind as a good example of very tight tolerance and brilliant locating keys that properly did their job.