I’m definitely shown to be better (8)
I believe the answer is:
improved
'to be better' is the definition.
('improved' can be similar in meaning to 'better')
'i'm definitely' is the wordplay.
'definitely' becomes 'proved' (I can't justify this - if you can you should give a lot more credence to this answer).
'im'+'proved'='IMPROVED'
'shown' is the link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for improved that I've seen before include "Grew or made better" , "Made better in quality" , "Made or got better" , "Made progress" , "Became better" .)