Larian Studios Forums Divinity - Original Sin Divinity - Original Sin - General Max level Blacksmithing is bugged.

High level blacksmith items can come with small boni. For 2H axes this is additional damage or critical hit chance. If you get the additional damage version, you can't improve that damage any further with the whetstone, making the crit version superior (although the nominal damage of a sharpened crit axe is still lower, the additional crit damage makes up for it).