The solvent is a structureless dielectric

This suggestion is manifestly untme. The solvent consists of molecules which have structure. The only respect in which the theory takes account of this is the modification of the electrostatic interactions by the solvent through the macroscopic relative permittivity. This is a crude attempt to recognise the importance of the ion-dipole interactions which undoubtedly occur. To cover more physically realistic situations the model needs considerable modification to include  

The complexity of the mathematics has meant that these features of the dielectric properties of the solvent have not been incorporated into a new development and suggests that a new model is required (see Sections 10.16, 10.19 and 10.21). 

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