Article by this writer’s not so lacking in purpose (7)
I believe the answer is:
aimless
'lacking in purpose' is the definition.
(without aim or purpose)
'article by this writer's not' is the wordplay.
'article' becomes 'a' (the indefinite article in English).
'by' is a charade indicator (letters next to each other).
'this writer's' becomes 'I'm' (the person writing the crossword clues).
'not' becomes 'less' (I've seen this in other clues).
'a'+'im'+'less'='AIMLESS'
'so' acts as a link.
(Other definitions for aimless that I've seen before include "Without direction or ambition" , "With no plan or programme" , "Lacking ambition or target" , "Melissa (anag) -- unmotivated" , "not knowing where to go?" .)