Though excellent, are not such good duplicates (9)
I believe the answer is:
matchless
'though excellent' is the definition.
'matchless' can be an answer for 'excellent' (thesaurus). I am unsure of the 'though' bit.
'not such good duplicates' is the wordplay.
I cannot quite see how this works, but
'not' could be 'less' (I've seen this in other clues) and 'less' is found in the answer.
The remaining letters 'match' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'are' acts as a link.
Can you help me to learn more?
(Other definitions for matchless that I've seen before include "Having no equal" , "team without a fixture" , "Incomparable" , "Unbeatable" , "Unique" .)