dr. carey reams spent years developing a chart which shows what are the target brix readings for hundreds of different types of produce, those following his techniques still use those charts.
This is very different from your original assertion that high brix is good. If you are accurate about Carey, then he has given each food has a target value (more likely range) and higher is not better. Again my example about apples varieties is perfect, simple going for the highest number for every variety would be wrong. Every variety has a specific value that may be optimal, so just getting value X is meaningless.
As I wrote brix may be of value when comparing a single crop from a specific field, if you know what value you are looking for then it is an easy way to measure when to harvest
We should also keep in mind that the farmer and consumer have different goals, the farmer wants to maximize his crop, sales and reduce spoilage during transport. The consumer wants cheap, healthy, unspoiled food. So if a farmer is using brix to reduce spoilage it may not alway represent the optimal nutritious choice for the end user.
Imagine two identical apples from the same vine that have the same brix value, but exposed to a cold wind for a couple of days one apple shields the other, the result is one is slightly dehydrated. The result is that the dehydrated apple would test a higher Brix value. By your measure this would make it "better", again a simple example that illustrates the problem with using brix values to determine "goodness"
There is a reason why in universities chemistry majors devote several semesters to learn about analytical and quantitative methods, it is never as simple as measuring a single factor. It is always more complicated.