I've been thinking about this myself recently. Orc's Bane really is a strange weapon.
I tried running some numbers on Orc's Bane and came to the conclusion that it is almost as effective against an Orc as a Battleaxe. Here are an Orc's chances of surviving being attacked by a few different weapons.
| Shortsword | Broadsword | Battleaxe | Orcs Bane |
| 41% | 25% | 15% | 17% |
So Orcs Bane really is effective against 'an Orc'. The problem is it's next to useless against any other monster, but I think we all knew that already.
EU players can hand Orcs Bane to the Wizard (
Glamdring anyone?) which gives it an additional use as he is limited to 2 attack dice anyway. But for any other Hero I don't think it is really worthwhile.
Your solution is interesting and will make the weapon relevant in quests that don't feature Orcs but the weapon is still going to be next to useless against a lot of monsters in any quest.
So, as I said, I have been thinking about this issue myself. As I'm not keen on rewriting official content I came up with a slightly different solution.

The wording on this one is still a bit clunky and it needs to restrict the use of a shield when being used with another weapon. But you can see where I'm heading with it.