What David achieved with good fortune protecting one colonist (5-7)

I believe the answer is:

giant-killing

'what david achieved' is the definition.
(as in David and Goliath)

'good fortune protecting one colonist' is the wordplay.
'good' becomes 'g' (abbreviation).
'fortune' becomes 'killing' (making a killing is making a lot of money).
'protecting' is an insertion indicator (inserted letters are held or protected).
'one' becomes 'I' (Roman numeral).
'colonist' becomes 'ant' (I've seen this in another clue).
'g'+'killing'='gkilling'
'i'+'ant'='iant'
'gkilling' placed around 'iant' is 'GIANT-KILLING'.

'with' is the link.

I've seen this clue in The Guardian.

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