Implications of the phonemic/chronemic grouping of English vowels

A phonemic transcription is generally agreed to be the most convenient for practical teaching of English to foreigners and for many other purposes. As far as the representation of the English vowel system is concerned, such disagreement as there is appears to centre around the determining of the number of vowel phonemes. The matter has been complicated in English by the fact that certain pairs of vowels are said to differ through a complex of quality and quantity. In this way Professor Daniel Jones reduces a 21 vowel phoneme system to one of 11 simple vowel phonemes and 5 complex phonemic/chronemic groupings (also treated as 5 phonemes). An English vowel system is, therefore, established of 16 phonemes. Two questions seem to be raised by the introduction of these complex groupings: 1) While the chronemic distinction is certainly present, can it be said to be significant in the language? And, if it is significant, is it of greater or smaller importance than the purely qualitative distinction?