Steven,
While I agree that the proper coverstock is a more simple choice to make than the proper drilling, which can get complex, it is still more important. If you make a mistake, often a cover change cannot make it right, which was one point I was making with the oiler example.
Yes, if you are in the right neighborhood of having the correct coverstock, then minor surface adjustments can make the ball react properly. Like, in your Savage example. If you bought the Pantera instead of the Savage for medium to medium-heavy oil pattern, then you'd probably still be in good shape.
But also, using your Savage example, I wonder if everyone can make the same use of it as you did. As I stated before, not every cover is that versatile. (Also, I am not a believer in taking a dull, sanded ball to a superfine 2000 grit and then polishing it up to use on 2 levels less oil than it was intended, UNLESS you made a big mistake, or were sold the wrong ball by your driller or some other serious cause preventing you from buying the right ball for that condition. Yes, sometimes there are balls and release that allow that, as your Savage allowed you to do.)
On the other hand:
"However, if I get the drill pattern wrong relative to my speed/release, I have a major problem. "
While other drill patterns may be better suited, if you have the right cover, something can almost always be done. The hook shape is not an essential for the vast majority of people. Actually, for extremes of very heavy oil to very light/dry conditions, I wonder just how important a drilling is, if at all.
As we get closer to the huge variety of medium conditions, I think we all get more and more fussy about the way we want the ball's path to look. For those of us more fussy, myself included, for those of us spoiled by excellent drillers, I think the right drill pattern on the wrong ball is worse than the wrong drill pattern on the right ball.
The 70/30 rule is just a generic label, a way to reference the ratio; I'd wonder if it's ever 70/30. It might be as low as 15/85 or it might be as high as 45/55, for some newer, very fussy balls. I think the bell curve has its effect here with more clustered around whatever is the true number.
As far as our discussion here, unless we tested a huge number of balls and a huge number of drillings, I think we each can site examples and we can say how we feel about the way balls and drillings have affected how we bowled. But I think, in the end, neither of us will have proof enough to satisfy the other. It just comes down to a feeling, after doing x number of drillings and Y number of surface changes. It may be one of those moot points we come across in bowling every so often.
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"We get old too fast, and too late, smart."