Most poetry ever written probably follows that percentage, and that definition.
I'm going to make what might be a bold statement here:
Most art is garbage, even the educated stuff (sometimes especially the educated stuff). Take classical music for an example (as it's my main focus). There are thousands of composers writing music right now. Maybe one of them will be remembered in 100 years. Even of the people we think of "Great 20th century composers", Copland, Shostakovich, Prokofiev, Gershwin, Shoenberg, Ellington, and others, perhaps two or three will be remembered and celebrated in the way that we remember and celebrate people like Bach and Mozart. Even then, not everything the "Masters" wrote was great- Beethoven's "Wellington's Victory" has generally been seen as awful from the moment it premiered.
You have to run under the assumption that most of the art you will ever see created in your lifetime with be crap, and even the stuff that will be good will be forgotten, just like every other age. Museums can make this deceptive, showcasing the greatest art from 500 years and more, but it's not that those people didn't have to deal with crap. It's that the crap has dried up and blown away, leaving (mostly) the good stuff.
So what i'm saying is that your statement is correct, but it is also correct for every other era of poetry, and every other kind of art.