Martin (1992: 490):
Because of this, grammatical metaphor is linguistics' most important tool for understanding discourse semantics as research is developed beyond the systems and patterns of interaction proposed here — and for understanding the relation between texture and context. It is thus the key to understanding text in context — to contextualising the ineffable.
 The discourse semantics model does not provide a means of modelling grammatical metaphor, and the notion of grammatical metaphor in the model is largely misunderstood, as repeatedly demonstrated in the critiques here.
A major shortcoming of discourse semantics, with regard to grammatical metaphor, is that it doesn't provide the semantics (meanings) that are to be realised either congruently or metaphorically in lexicogrammar (wordings). For example, with regard to ideational metaphor, it doesn't provide the equivalent of a figure (Halliday & Matthiessen 1999), that is realised either congruently as a clause, or metaphorically as something else, such as a nominal group serving as a participant element of clause structure. Martin (1992: 325):
The level of discourse semantics is the least developed as far as ideational meaning is concerned. This is mainly due to the fact that the description developed here has focussed on relationships between experiential meanings, rather than the experiential meanings themselves.
A second major shortcoming is the fact that much of logical discourse semantics is merely a mislabelling of expansion relations — projection is omitted from the model — with no regard for whether they are deployed logically (structurally) or textually (cohesively). This sets up incongruent realisations where there is no metaphor. For example, in discourse semantics, the logical relation in
- Ben can train hard without improving his time
is said to be concessive purpose (p199), whereas, in lexicogrammar, the relation is adversative addition. That is, concessive purpose is incongruently realised as adversative addition. This is incongruence, but not metaphor.
 There are texts that don't involve the deployment of grammatical metaphor. For these, the relation between texture and context can, nevertheless, be understood. Thus grammatical metaphor is not key to understanding text in context.
 In the words of Conan Doyle's Dr. John H. Watson: "What ineffable twaddle!"