Does an inconsistent roast affect espresso extraction? If so, how? I'm not really asking about flavour, I understand that an inconsistent roast causes  inconsistent flavour. 

My question is how it affects the extraction itself. Does an uneven roast lead to an uneven extraction? Or does it not really matter?

We can assume other variables are consistent, i.e. a good tamp and a consistent brew temperature within the ideal range for espresso extraction.
That's a tricky one.
It depends on what do you mean by 'extraction'.

&quot;Coffee extraction is the process of dissolving soluble flavors from coffee grounds in water&quot; - from Wikipedia.
&quot;Extraction is everything that the water takes from the coffee&quot; - from BaristaHustle.
&quot;To remove or take out something&quot; - from Cambridge dictionary.

Therefore, the extraction process considers dissolving the flavors. An uneven roast will affect directly the flavours on the final beverage. Thus, even the perfect extraction will not be able to extract all the flavours it could if the beans weren't correctly roasted.