Well, I can calculate it, I just won't because you're basing it on something entirely different than the reality of the game. Kind of like the gamblers fallacy that something is "due" because the opposite has happened X number of times in the past. My math covers ALL possibilities.
1st, shield only works on 20% of attacks and only if those attacks are in the 73% of AC/Reflex attacks. This is EXACTLY 14.6% chance that each time a wizard is attacked shield can be of use.
2nd the halfling power works on ANY attack but only changes the outcome about 50% of the time. This is roughly a 25% chance that each time the wizard is attacked the reroll power can help. PLUS the halfling attack is 95% likely to remove a crit. AND as an additional bonus (pretty hard to compute the exact math number) it can block attacks that are vs will and fort which are vastly more likely to have an additional effect than attacks vs AC.
Ok, let's use your numbers 14.6% for Shield.
25% for Second Wind.
Let's use the case that the Wizard gets hit.
Since he only gets hit 50% of the time of all attacks (using your math here), his chance of stopping an attack is 29.2% for Shield and 50% for Second Wind (the same numbers I posted earlier).
He has to get attacked first to even use the powers. Getting missed does not do anything for these powers.
So, let's take DM adjudication 2E above where the DM tells the player exactly when Shield works and exactly when it does not.
Let's say that the Wizard gets hit 1 time in an encounter.
If he uses Second Wind, he takes (on average) 50% of the damage of the hit or 50% damage.
If he uses Shield, his odds of getting hit are:
70.8% (100% - 29.2%, Shield did not work because it was a Will attack, a Fort attack, or a AC/Reflex attack roll that Shield would not stop) of the damage.
So, do you agree that with DM adjudication 2E, for a single successful hit in a round, Second Wind (50% of the damage) protects better than Shield (70.8% of the damage)?
That's the exact same ratio as your numbers (25% of not getting hit vs. 14.6% of not getting hit), it just ignores the silliness of talking about all attacks. It's really 50% vs. 29.2% of the first successful attack since the attack has to hit in order for Second Wind or Shield to work at all.
But, what if it is two successful attacks hit (in different rounds) in an entire encounter instead of one (this is where your math stops)?
If he uses Second Wind, he takes 50% of the damage of the first hit and 100% of the damage of the second hit, or 150% damage.
If he uses Shield, his odds of getting hit both times is 70.8% first hit * 70.8% second hit = 50.1264% * 200% of the damage. His odds of only getting hit once is 49.8736% * 100% of the damage.
Or, 50.1264% * 200% + 49.8736% * 100% = 150.1264% of the damage.
For all intents and purposes, TWO successful hits in an encounter averages virtually the same damage with Second Wind and Shield. And, this does not even take into account the bonus Shield has with lasting to the end of the Wizard's next turn (note: I used the example of hits on two separate rounds above).
What about 3 successful attacks in the same encounter?
Second Wind does 250% damage (50% + 100% + 100%).
Shield does 70.8% first hits * 70.8% second hits * 70.8% third hits = 35.4894912% * 300% + 64.5105088% * 200% = 235.4894912% of the damage.
With one successful attack in an encounter, Second Wind works better (as you keep claiming).
With two successful attacks in an encounter, Shield has a very slight edge (since one or more AC/Reflex attack can occur in the same round, lasting until the end of the next turn edges this towards Shield, but only ever so slightly).
With three or more successful attacks in an encounter, Shield wins.
The reason this works is because if Shield does not work (with the 2E adjudication) on an earlier successful attack, the Wizard still has it as an option for a future successful attack in the same encounter until it does work.
This is using YOUR percentages (which also happened to be mine in an earlier post).
Are you starting to understand now how your numbers were limited to ONE and only one attack in an entire encounter? Your numbers were great for that. But, your numbers ignored the fact that if Shield cannot be used, then it is still available for use later in the encounter.
One has to look at the bigger picture.
And to be honest, 2E is starting to sound reasonable to me now that I have run the math for it for multiple successful attacks.
But, 2E Shield is better in the long run than Second Wind unless your Wizard averages getting hit by 1 or fewer successful attacks per encounter. I really doubt that happens in most games.
Note: I do not discount the fact that Fort and Will attacks have additional effects. However, Reflex attacks also often have additional effects such as ongoing damage, so Reflex attacks cannot totally be discounted either.