OK, I should have said national bias rather than racial I suppose, (it was getting late). The offence remains - particularly since Elting was talking out of the wrong part of his anatomy in that quote: English writers have largely ignored Macdonald since he didn't serve against them in the Peninsula. Sir Walter Scott (not English) who knew him personally, gave him a good write-up which has tended to carry over but the highest praise has always come from French writers.
As I see Digby has already pointed out, the swampy ground is actually irrelevant since no-one was suggesting a full length causeway should have been built. It was the numerous streams and rivers in the area (which were presumably draining the marshes) which were causing the problems.