KarinsDad said:I put your equations into a spreadsheet. For 2 attacks, it comes out to 9 to 16 needed on the die advantage Displacement, 8 is more or less a tie (the break even point), and 17+ and 7- are advantage Shielding Smite.
The highest percentage advantage was about 19% (less average damage) for a 14 or a 15 needed to roll (for an attack that does 10 points, this means 8 points instead of 10 on average, not a huge gain).
An important note is that since 4e has supposedly "fixed" the math, then in an average fight most monsters will need around a 9 to 16 to hit the party members (I believe the 55%-60% mark was noted in some designers comments). So considering that, displacement will have the advantage more often than shielding smite.
However, KarinsDad's point about being hit twice is an important one. In many cases, a wizard might survive one hit, its getting hit twice in one round that can be a killer.
Finally, consider when we are discussing the difference between displacement and shielding smite, we are talking about one class which is a "defender", a holy class designed to guard, vs a "controller", designed to effect and influence the battlefield. Even if shielding smite compares to a much higher level spell, that's an important distinction.