The notion that a reliance on lyrics is a modern thing is utterly wrong, I must say. It was a cornerstone of the late renaissance and early baroque. Composers like Monteverdi and Caccini stressed time and time again the the music must serve the text. In setting poetry by such fantastic writers as Tasso and Petrarch, they came up with the most incredible effects by disregarding all of the "rules" of music in order to emphasize the affect of the words.

Even a lot of the instrumental music of this period shows a lot of the same influence - it relies on a "speech-like" sort of cadence, with the same constantly changing emotion that can be found in the poetry.

This idea of music's subservience to text let to the development of opera. The musical theatre of the 17th century is a far cry from the relatively static set pieces of Handel, and even Wagner. The music twists and turns as it tries to follow the chaos depicted in the text, giving each word a specific colour. It's really rather similar to rap, only instead of disregarding the music entirely to allow the words to come through, the music simply becomes simplified and extremely flexible, so that it can follow the words wherever they might go. In some cases, you even see the same sort of repetitive musical accompaniment to the words that rap has, for example in Monteverdi's Lamento della Ninfa.

So just because the 18th and 19th century saw a lot of large-scale instrumental music, don't think that lyric-centric music is a modern invention. Examples like this abound in music history, from medieval troubadour songs right back to Aristotle's poetics. Poetry and music have always been linked, and will probably continue to be.