He stole the concept of poetry from Yeats?

Those aren't nearly close enough to be considered stolen. Possibly allusions (which is not stealing), but even then, the only similarity of the bests is "The best" usage. Nothing about the rest of the lines, or before, are similar enough to be "stolen" (potentially the Ginsberg troping Yeat's "full of passionate intensity" of the worst into his best's "madness, starving hysterical", but that too is allusion, not stealing).

The best lack all conviction, while the worst // Are full of passionate intensity.

vs

I saw the best minds of my generation destroyed by madness, starving hysterical naked, // dragging themselves through the negro streets at dawn looking for an angry fix,

How is this stealing in any form?