Perfect though said to lack foundation (8)
I believe the answer is:
flawless
'perfect' is the definition.
(similar in meaning)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for flawless that I've seen before include "Perfect, without defect" , "Without blemish or imperfection" , "sinner isn't this" , "Pristine" , "Impeccable" .)