So, I finally decided to bite the bullet and go through the math on how good Luke's ability is. Since a result of EFF (Evade Focus Focus) is the same as EEB as well as EFB, it's much more complicated than all of the other results.
So, rolling 2 evade dice without a focus results in .75 evades. With a focus, this is increased to 1.25, but you can only have 1 focus action (though you can get up to 3 focus tokens). Luke's ability grants him 1.19 evade, almost as good as the focus action. But lets take it a step further - how survivable can you make Luke?
If you give him R2-F2 and a Stealth, he is rolling 4 Evade dice, but his action is spent on R2-F2. This results in an average of 2.18 Evades being rolled. When the Stealth is finally stripped, he is down to 1.70 with just R2-F2. This compares to 1.50 and 1.13 for a standard X wing. Which means that Luke's ability gives him around 50% more evades than a standard X wing. While this number varies depending on number of dice, it ranges from 36% at 6 dice to 67% at 1 die.
So that's all fine and good. 50% additional evasion is great. When you look at the effective health of an X wing, which is the total health (hull+shields) divided by the expected damage received per attack, Luke has almost twice as much effective health.
X Wing effective health vs. 2 attack dice = 9.8
Luke effective health vs. 2 attack dice =
18.2
X Wing effective health vs. 3 attack dice = 5.7
Luke effective health vs. 3 attack dice = 8.6
X Wing effective health vs. 4 attack dice = 3.8
Luke effective health vs. 4 attack dice =
5.2
So... now we have a baseline to measure his ability. Let's compare it to taking an extra shield. If we ignore the +4 PS, a Red squadron w/ Shield upgrade is 27 points, and Luke is 28 points (but has 4 extra PS). Close enough for a comparison.
X Wing w/ Shield vs. 2 = 11.8
X Wing w/ Shield vs. 3 = 6.8
X Wing w/ Shield vs. 4 = 4.5
From this, it's very easy to determine that if you are debating between an X wing with a shield or Luke, if you have the 28 points to fit him into your build, you should. The follow up question then becomes do you put a shield or stealth on Luke? And what about R2-F2 or R2-D2?
A Shield increases his effective health to:
vs. 2 attack = 21.9
vs. 3 attack = 10.3
vs. 4 attack = 6.2
Which basically averages out to making him live through an additional two attacks. R2-F2 increases his effective health to:
vs. 2 attack = 35.7
vs. 3 attack = 14.2
vs. 4 attack = 7.7
If we do some fuzzy math, we can come to the conclusion that it will take 7 2 dice attacks , 3 3 dice attacks, and ~1.5 4 dice attacks to strip the stealth device. So then the stealth device provides the follow approximate effective health:
vs. 2 attack = 21.6
vs. 3 attack = 9.8
vs. 4 attack = 5.6
It would seem that by itself, the shield is still better on Luke than the stealth device. As for R2-D2 vs. R2-F2... each shield R2 regenerates tachs on 3.6/1.7/1.0 attacks from 2/3/4 dice. Which means that R2-D2 vs. R2-F2 is very dependent on what's attacking you... against 4 dice, if you regenerate 1 shield, you're already ahead. But against 2 dice attacks, it'll take 6 shields to match up. Don't forget that R2-F2 requires an action, and R2-D2 requires a green maneuver, each has it's own drawback.
But what about the ultimate dodging X wing in Luke + R2-F2 + Stealth? With 4 evade dice, Luke's effective health is 68.7/23.5/11.5. Which means it'll take ~13/5/2.4 hits to strip the evade die. Which means the fuzzy math puts his effective health at:
vs. 2 attack = 41
vs. 3 attack = 16.4
vs. 4 attack = 8.5
But this STILL comes up short compared to R2-F2 w/ Shield, which puts his effective health at:
vs. 2 attack = 42.8
vs. 3 attack = 17.0
vs. 4 attack = 9.2
So, what conclusions can be drawn from this? First off, the only ship that has more effective health than Luke is the Firespray (I didn't compare the other ships here, but it's true) Second off, for a pure point value point of view, it's better to take Luke over an X wing with a Shield. Third, the stealth device isn't quite as good as a shield, but only costs 3 points, so point for point it is better than a shield on Luke. Finally, R2-D2 is the better choice than R2-F2 against everything but swarms, though that doesn't take into account the positioning / predictability of the ship, or the loss of an action.
tl:dr - Luke is the best X wing due to his much greater defenses. He will live through twice as many shots as Wedge, which means he'll be around at least twice as long as Wedge, and therefore can do more damage in the long run.