All facts show us that comparison of lexicon is completely irrelevant methodology in the field of historical comparative studies of languages.
Why we can say that language is first of all grammar, i.e.: system of grammar meanings and their distributions but not a heap of lexemes?
Yet William Jones, founding father of linguistics, pointed on the fact that grammar is much more important than lexis:
The Sanscrit language, whatever be its antiquity, is of a wonderful structure; more perfect than the Greek, more copious than the Latin, and more exquisitely refined than either; yet bearing to both of them a stronger affinity, both in the roots of verbs, and in the forms of grammar, than could possibly have been produced by accident; so strong, indeed, that no philologer could examine them all three without believing them to have sprung from some common source, which perhaps no longer exists. There is a similar reason, though not quite so forcible, for supposing that both the Gothick and the Celtick, though blended with a very different idiom, had the same origin with the Sanscrit; and the old Persian might be added to the same family, if this were the place for discussing any question concerning the antiquities of Persia (Jones 1798: 422 – 423).
Main function of any language is to be mean of communication, but in order to be able to communicate we have to set a system of rubrics/labels/markers first of all, that’s why main function of any language is to rubricate/to structurize reality. Structural level/grammar is the mean that rubricates reality and so it is much more important than lexicon. I suppose we can even say that structure appeared before languages of modern type, i.e.: when ancestors of Homo sapiens developed possibility of free combination of two signals inside one “utterance” it already was primitive form of modern language. Structure is something alike bottle while lexicon is liquid/matter which is inside the bottle; in a bottle can be put wine, water, gasoline or even sand but the bottle always remains bottle.
To those who think that structure is not important I can give the following example taken from Japanese language: Gakusei ha essei wo gugutte purinto shita. “Having googled an essay student printed [it]”. What makes this phrase be a Japanese phrase? “Japanese” words