Agreed, in general I'd think you'd want the Petal in the main hand. Even if you don't use any Ranged powers, the better damage type alone is considerable, and that Blessed buff is crazy good, certainly way better than 15% extra damage that only triggers on a crit.
Sickle's a pretty good weapon, half the damage is Raw for some reason and it's got 10 Armor Penetration while the Balanced Blade has none.
I think it would take a very high Accuracy/Crit build to make the Balanced Blade worth it, and even then I suspect the Short Sword might almost always be better. It's silly but while the Balanced Blade's special effect is "Deals 15% more damage on a crit", the Short Sword's higher base damage essentially means its special effect is "Deals 17% more damage on a crit and 17% more damage on a hit" which is obviously way, way better. It does have much less Accuracy, but more Armor Penetration.
It's quite remarkable how strong the basic weapons are.