Tourist,
Who says there is a problem with Merlin downdraft? What report and by who?
Not only does he maths on that statement, look pretty dodgy, (remember SAR- NOT troop lift weights) but Canada did not agree and not did Portugal. I believe that reports have shown that Merlin has less downdraft at operational weight, than a Puma or a SeaKing.
I haven't got time to sit down and re-do the maths, but give it a go yourself and tell me what you get.