Read the quote, Richie!
You are neglecting what the ball has to roll over as a factor...not all surfaces are the same in terms of speed, and slope.
So for some, varying the sw 'carry' is the more consistent option.
Read my quotes in regards to green speed and slope:
'The rollout is figured out for you
if the stimpmeter is of a decent speed and you're not on a very uphill or downhill lie (slower greens may require more club than the Rule of 12 dictates, faster greens may require less club, etc.' -
Richie3Jack
and
'Found a neat little sidebar to the Rule of 12.
You can use it to get a good idea of the speed of the greens. If you go to the practice green and find a relatively flat service and execute the chip shot properly, if the ball goes way short and you need to use extra club, then you know the greens are slow. If the opposite happens, then you're playing on some faster greens.' -
Richie3Jack
So, you do have to take those factors into account. If I'm doing the math and I've got a 7-iron and the green is slow and/or the slope is uphill, I may want to consider chipping with a 6-iron.
But if you can get the speed of the roll down somewhat, then I think it's much easier to hit say an 8-iron to a safe zone that is only 3 yards away versus hitting a SW to say 9 yards away (and hoping that the spin created with the SW is the right amount).
I do believe you have to go with what works best for you and usually being comfortable helps you execute better. But I believe there's a reason why the Rule of 12 is a very smart principle and if you're moving the safe zone to say 10 yards on the green instead of a 1 yard on the green, then you're really defeating its purpose.
3JACK