Theoretically, you should be able to outpace 4 damage per turn but SoW adds to an already brutally unforgiving deck...
That is the crux of the problem. Shard of Wisdom empowers an already working, but - let's be frank - uninspired deck. Against Mono-Ether, the basic problem is to get rid of the Dimensional Shields and outdo the damage made by the un-controllable creatures. Now, you still have to cope with the original problems,
plus Mono-Ether does even more damage which can't be reduced by most of the normal shields...
Put it in another way: who would hurray for a card which makes the life of a Ghostmare deck even easier? (Like, a Shard of Boredom, which turns an already played Time creature into Ghost of the Past...?) <--- same situation with Shard of Wisdom, I think.