WoW is this true?
Two serious mistakes were Ney's cavalry charge against the British squares, and Grouchy wandering around instead of hitting Wellington's flank or at least pushing Blucher out of the fight completely.
As to the British Army, it was loaded with hardened veterans of many campaigns and they were some tough hombres.
Wellington was smart to get the high ground, put many of his troops behind the slopeof the hill and fight a defensive battle.