I don't think "~1%" is a fair summary of that link, especially not "in the best case". You're trying to breakdown what happens to a 4% fee, and many of the airlines have miles valued at >2% at that link.
I also don't know where you're getting that 7 miles/dollar number from.
The 7 miles per dollar comes from the delta Amex marketing flyer sitting on my pile of mail, but I didn't look at the fine print, I got curious and looked into details : actually it's only 1 mile per dollar for usual purchases, you get one additional mile on "delta purchases", then you can get 5 extra more on money spent on flights itself. So yeah on average it's close to 1 mile per dollar, I can't edit the original post. So the math makes more sense with those numbers :)
I also don't know where you're getting that 7 miles/dollar number from.