I also did some research on the dual angle "sweet spot," and I'm honestly not sure that I like it that much. It's a bunch of information and calculation and considers too many variables only to get you a really wide range of options that still leaves everything completely up to you. I went through it a couple times and found myself right back where I started in the first place, with a lot of decisions to make.
This still leaves you with about the same amount of decisions, but a tenth of the process, but it honestly does apply and work AND it locks down the angle sum to a much closer range than the sweet spot does. Everybody factors in whether they're going to be playing straight up or deep into their layout and ball choice, and that's exactly what this is, it's just a way to be more accurate. I know where to put the fingers to get a ball to do what I want it to do without using the dual angle, it's just simply more accurate.
You're not going to play 2nd arrow with the same ball you play 4th arrow from unless several things change, but then you've significantly changed the parameters of everything to begin with. If you throw the ball 17 mph, 350 revs, 40 degree angle of rotation and 10 degree axis tilt from 2nd arrow, by the time you're forced into 4th arrow, if you're using the same ball, the lanes have gotten drier AND you've changed a lot of that stuff. That also however doesn't mean that another ball with a different drilling wouldn't be better suited for where you're playing now.
At the same time, I'm old school, I'd RATHER use the same ball all day long no matter what I have to do to it or make it do. HOWEVER, if we're talking conceptually only considering ideal situations, I can't poke a hole in this and have a reasonable explaination for every question, concern, or criticism.