No twisting of anything required - after 117 ODIs, Parore averaged over 30. In his last 62 he averaged 15. Simple as. No changing either of those things.
Yes, his strike-rate wasn't the best, but slow runs are better than no runs even in ODIs.
I know perfectly well that you think The World of McCullum, you've said it enough times, but the simple fact of the matter is that, capable of one 25-ball 50 every 90 games or so, he's currently nowhere near the level Parore achieved for much of his career. Maybe McCullum's ODI average will go up. If so, I'm sure you'll be delighted. Me, however, I'm not going to expect that at all. McCullum may still be young but he's certainly not early in his career any more, he's played a good deal and there's a perfectly conceivable chance he's shown us all he's got.
Tell me - if some 20-year-old wicketkeeper-batsman appeared next season and started scoring centuries in the top-order and managing a 50-plus average, would you start thinking about having McCullum replaced should his current form continue?