The essence of the matter is - good leader is tip-top (4)
I believe the answer is:
gist
'the essence' is the definition.
('gist' can be a synonym of 'essence')
'good leader is tip-top' is the wordplay.
'leader' suggests taking the first letters.
'tip-top' becomes 't' (top of the word 'tip-').
The initial letter of 'good' is 'g'.
'g'+'is'+'t'='GIST'
'of the matter is' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for gist that I've seen before include "The pitch on the matter" , "Pith, essence" , "Main points" , "Real point or substance" , "Main idea, kernel of matter" .)