Yes, but as I've already pointed out, Petrarch composed Africa. While I do believe that all of the poets you name with the possible exceptions of Cavalcanti and Traherne, whom I'm less familiar with, deserve to be ranked at least as highly as any of the Romantics, I'm not sure that they all surpass them. I would also like to float the hypothesis that no truly great artist succeeds to canonical greatness without attempting that one really big venture, the one that a minor talent could not even attempt, or if they did their mediocrity would show in every brushstroke.
Rilke is very accomplished at what he does, but every poem of his leaves me wanting something more. He is like a beautiful flightless bird. Everything is there which is required, except for one thing. He has rhythm, and diction, a capacity for depth and aphorism which never attains to real development. Each of his poems is like, "Here's an interesting thought I had." To which I'm like, "Yes, that is interesting. Would you maybe like to develop that thought further and see where it goes?" He's the premature ejaculator of modern poetry. As curious and visionary as his style is, it stops where Blake would just be beginning. His little bon mots are the sorts of things a really great poet would use as a point of departure and a way of springing into something altogether different. They should be gateways and he's using them as ends in themselves.
I'm not particularly interested in who the best writer was aged 25-30. I'm interested in their results. You can't know what they would have gone on to do, and I don't think we should calculate their promise in with the actual accomplishments which they did achieve. Buchner might have been the next Goethe if he'd lived past the age of 24. So what? He didn't. Personally, I believe Rimbaud's reputation would have suffered if he'd continued to write, but I can't know that for sure. Lot's of people's nephews write very well for a five year old. That is not what is at issue here.
By the time they were my age Moliere was a failed actor, Thomas Dekker was in prison, and Keats had been dead a year. Jesus Christ and Alexander the Great both croaked at 33. I'd better get cracking! This sort of age specific intelligence is perhaps useful as a guideline to the living, but not terribly helpful when it comes to judging art and ability.

