Having high output for short duration — one critic's conclusion (8)
I believe the answer is:
prolific
'having high output' is the definition.
'for short duration one critic's conclusion' is the wordplay.
'for' becomes 'pro' (I've seen this before**).
'short' means to remove the last letter.
'duration' becomes 'life'.
'one' becomes 'i' (Roman numeral).
'conclusion' suggests the final letters.
The last letter of 'critic' is 'c'.
'life' with its last letter removed is 'lif'.
'pro'+'lif'+'i'+'c'='PROLIFIC'
(Other definitions for prolific that I've seen before include "Rich" , "Producing fruit in abundance" , "Copious" , "Very fertile, productive" , "Plentiful" .)