Cadence and pattern. These become for Pound and the moderns the antidotes to stale phrases and metrics. And this is where today's poets make their mistakes. Free, they proclaim, is free from those old ideas and they leave it there. They forget to use the replacements. Their jumbles of words have no connections or no cadence. A framework must exist or all will be washed away to be forgotten. Those who count syllables may carry on for a time; they have established a pattern. However, unless that pattern is translated into a discernable cadence (which does happen in the best) such poems too become unmemorable. And unmemorable is not what a poem should be.
Sure, you can blame him for the ubiquitious "free verse" that he promoted in English poetry. He and his bunch began that thing about presenting "images" to say things rather than using good old flowery words and phrases arranged in metronomic feet and all that good old stuff. Read Shakespeare's sonnets along side Pound's Cantos: you'll have no idea what he's on about.
But already in the first decades of the twentieth century, the times they were a-changing (sorry, Bob.) Literature and poetry in English were stuck in a Victorian rut; what was happening was happening in Europe: wars and rumours of war, but also slashing decisive movements in art and literature. With the influences of French symbolism in poetry, Impressionism and Cubism in art, and Dada in everything, Pound and others began to work the new ideas into the English language, shaping some to their own use and creating others. The "Imagists" and the writers reflecting the crumbling of society began a new look in literature and the understanding of it.He encouraged and supported T. S. Eliot's poetry. Eliot's "The Wasteland" became the premier example of modernist poetry, using all the techniques and rationales the writers proclaimed. In the field of the novel, James Joyce worked these into Ullyses and later Finnegan's Wake.
Pound would use images to say only what they could. He used quotations in other languages, footnotes, other techniques foreign to poetry. He took these images and, instead of arranging them in nice orderly rows that fit together the way poetry had for ages, scattered them seemingly haphazardly on the page without any evident relationship. Instead of writing in accented feet, Pound wrote his phrases like musical phrases, holding true to a cadence and flow. What it ends up as seems to be an interlocking mass of words, hiding any sense and meaning.But with a critical look, the jumble of stones, the collage of different ideas and phrases, become more that what is first apparent. They point at and even carry a beauty of their own. Words and phrases, ideas and concepts, they begin to connect, to form random patterns as if tossed for the I Ching. Perhaps this is partly due to Pound's study and work with traditional Chinese poetry.