Hogeye, I respect your knowledge and your perspective, even though I think I disagree.
First, many super fancy guitars have grain runout on the tops. Now, I don't know much about carpentry and wood, but from I've read, this is an avoidable problem: If you split the wood instead of sawing it this is not a problem. http://www.lutherie.net/frankford.runout.html
And yet Martin, Gibson, and Taylor don't try avoiding this. Probably because they are not boutique builders and don't want to take the time to avoid this. Tops with runout are more fragile than those without and yet many elite guitars have runout, and don't wind up imploding.
Now, regarding your main point i.e. the fragility of flat-sawn wood. It's hard for me to imagine that flat-sawn wood is more fragile than Brazilian Rosewood, which from what I've read, is fragile and susceptible to cracking: http://www.guitarnation.com/articles/calkin.htm
Brazilian is still the most desirable tonewood despite this.
Also, I think there is a very fine line between a workhorse and a budget guitar. Doubtless, there are some shortcomings strictly due to cutting costs that one finds in a J-45. The flubber pickguard is there too, there's a whole bunch of tusq instead of bone. It's got the Grovers that a lot of people don't like. (Is the problem you mentioned only with mini Grovers or all Grovers?). And yet it sounds great, and has become an icon.
I don't know as much as you do, and you seem to see the flat-sawn nature as unforgivable. Maybe you are right. But I think that when we buy a Gibson, even a J200 there will be some shortcoming vis-a-vis the craftsmanship that you don't get in, say, a Santa Cruz or a Goodall.
I think it is called the J-15 not because it's 1/3 of the J-45, but because it costs $1500. Kind of like a 21st century workhorse, a subtle nod to the J-45 and J-50 that cost 45 and 50 dollars.
In the above article about tonewoods, the author is fond of English Walnut, but he is also quite fond of the walnut one gets on the West Coast in the U.S.A.