Actually Justin I think he is totally wrong, I know I speak heresy, but think about it, if he is right then word painting should be the be all and end all of singing. The other down side of his statement is that it only encourages singers to spit out the consonants and overdo the vowels at the expense of the musical and verbal comprehension.
What music does is to transmit the underlying emotions, feelings and thrust of the argument that the composer has experienced in the text as he read it and then came up with a musical work that expresses what is in the poem/text.
The composer expects that his interpretation of the text and it’s qualities should be sung and not declaimed unless he decides otherwise, so the singer should first sing the musical phrase as the composer conceived it and attach the words without unduly emphasising the words unless otherwise indicated by the composer.
Since the quality of singing declined over the last 100 years we hear far more declamation than singing coupled with the blandest of bland voices sung with aggression and an absence of real colour when required.
Every time I see a masterclass I only ever see discussions about pronunciation and understanding of the poet’s text, never a discussion about what the composer wants from the singer from the composer’s understanding of the text, whether that be right or wrong, which is of course irrelevant to the performance of the song.