Severity of lead guitar on Blackbird - messy intro and outro got cut (9)

I believe the answer is:

graveness

I'm a little stuck... Click here to teach me more about this clue!

'severity of lead guitar' is the definition.
The answer and definition can be both human attributes as well as being singular nouns.
Maybe you can see an association between them that I can't see?

'blackbird messy intro and outro got cut' is the wordplay.
I cannot quite see how this works, but
'blackbird' could be 'raven' (I've seen this in another clue) and 'raven' is present in the answer.
This explanation may well be incorrect...

'on' acts as a link.

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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