The favourable slant is overwhelming a stage performer (8)
I believe the answer is:
thespian
'stage performer' is the definition.
(I've seen this before)
'the favourable slant is overwhelming a' is the wordplay.
'favourable slant' becomes 'spin' (as in political spin).
'is overwhelming' is an insertion indicator.
'spin' enclosing 'a' is 'spian'.
'the'+'spian'='THESPIAN'
(Other definitions for thespian that I've seen before include "Stage actor" , "Actor - neat hips (anag)" , "Dramatic actor" , "Actor; relating to drama" , "Relating to the theatre" .)