ab, brilliant, ta.
I've come to the conclusion that this was one of those crosswords that I simply disagree with.
If they'd put 'Out fox', or 'Bamboozle' for that clue for instance, then maybe I'd have sympathy for the answer.
But 'Make mincemeat of' - in my book - means some like 'Grind to a pulp', or 'Shred to pieces'