And yet isn't 'Beyond Good and Evil' ALSO poetic?
The whole work finishes with an actual poem, while the chapters tend to culminate in prose poems of dazzling word-play.
And the Preface ... if that is not poetic, I don't know what is!
No, we cannot say that 'Zarathustra' is poetic and 'Beyond Good and Evil' isn't; - they are BOTH poetic.
Isn't poetry very close to philosophy anyway?
Weren't Nietzsche's favourite Presocratics oftener than not, poets?

Poetry and philosophy began in the same ancient place, and merely split off into two streams; with Nietzsche they became united once more.

No, no - we cannot make 'poetry' as our difference between the two works; rather Nietzsche was wearing a different persona in BGE - he was speaking in another poetic voice; more Dionysus the philosopher-god, than Zarathustra, the teacher of the over-man.

Actually both works do not deal with the same ideas - Zarathustra concentrates on The Eternal Return and the Superman, whereas BGE concentrates on the decadence of European culture.
Quite different.

I think it is on record that Burckhardt did not really appreciate Nietzsche's 'Philosophy of the Future', much to Nietzsche's chagrin.
It seems that the philosopher tried to 'entice' the historian Burckhardt to read his books on the basis that by reading one he would understand the other.
As we know from actually READING BGE and TSZ this is a gross over-simplification that we can excuse Nietzsche [and Nietzsche ONLY] for.

Nietzsche's primary quality for me is 'the fragment'.