Perfect length for poetry?

[milo]

I think Endymion may be a tough choice because Keats wrote it at 19 and it’s quite dull reading
The mature Spenser was far better than the early Keats, but even he couldn’t make the faerie queene readable, except in parts here and there. Because it rhymes.

In his later Hyperion Keats achieved a mastery exceedingly Milton, IMO. And it’s much more readable than Endymion, being  blank verse, though only a fragment of the whole was actually written

I disagree but it's irrelevant to the discussion of length