Identifying the psychological/cognitive ability underlying achievement difficulties - important or redundant?

During the summer I ran into this article:  Psychiatrists split on whether to ditch DSM by Antony Funnell,  which  deals with the debate in the psychiatric community concerning the DSM5.  This article enlightens an aspect related to an issue that was discussed here – the relations between cognitive abilities and reading, writing and math achievement.  Funnell writes, that psychiatrists around the world, led by the US NATIONAL INSTITUTE OF MENTAL HEALTH are in open revolt against the DSM5, demanding that psychiatry be based on science and not on conjecture.  Traditional psychiatry, these psychiatrists say, relies too much on diagnosis based on symptoms  and  clinical observations .  Treating people coping with psychiatric conditions by the symptoms they present is not reasonable, just as it's not reasonable for a physician to prescribe the same medicine for everybody who feels chest pain, regardless of the pain's reasons: heartburn, a   muscle spasm or cardiac arrest. 

Here we reach the differences between SLD (specific learning disability) definition according to CHC theory, as developed by Flanagan, and SLD (specific learning disorder) definition according to the DSM5.  The essential elements of both definitions are presented here, along with the main differences between them.

As written in the presentation, Flanagan's definition requires linking the symptoms (the difficulties the child has in achievement) to the psychological/cognitive disabilities that lie at their base (empirically or reasonably).  The developers of the DSM5 definition, represented here by Rosemary Tannock, write in the DSM5 text, that specific learning disorder is "a neurodevelopmental disorder with a biological origin that is the basis for abnormalities at a cognitive level that are associated with the behavioral signs of the disorder".  But they argue that the relations between deficits in psychological/cognitive processing and reading are not proven enough (they are probabilistic and not deterministic).  That is, it's not possible to use a specific cognitive profile to confirm or reject the diagnosis of  a reading learning disability disorder, and the psychological processes underlying math and written expression difficulties are not clear.

The proponents of the CHC/Flanagan definition would agree with the claim, that learning disability cannot be diagnosed only on the basis of the child's cognitive profile.  Even if the cognitive profile shows difficulties, as long as they don't affect the child's daily functioning in the achievement domains (reading, writing, math), the child cannot be diagnosed as learning disabled according to this definition.

If the cognitive profile is not enough to diagnose learning disabilities, why is it needed at all?

It's evident, that treating and addressing the symptoms only (that is, remediating reading, writing or math directly)  - only partially   alleviates the problems in learning disabled children.  If we could prove in a   convincing way, that treating the cognitive disability improves the child's achievement in reading, writing or math, we would be able to say that identifying the cognitive/psychological difficulty underlying  the lowered performance in the achievement domains, will help us   plan an intervention that will assist the child more than treating the symptoms only. 

Our goal should be, in my view, to strengthen that evidence base (of the relations between treating/strengthening cognitive abilities and improvement in the achievement domain) so that we'll be able to reach an evidence based diagnostic practice.  Otherwise, the diagnosis of learning disability will remain an empty and a general lable,  that is not conducive to efficient treatment for the specific   child being diagnosed.