The chief difficulty in merging common sense to this rule is a misperception of combat time.
Per RM rules. . .luke went frenzy, and made. . .one melee attack roll at full OB.
Keep in mind the 10 second round, and a lot of this makes more sense.
The odds of rolling one open ended up result out of seven rolls is not great, the odds of doing it on one roll are 5%. . . .so vader failed. . .
Also, a basic break between common sense, real world melee combat and RM combat.
Real world: Dodge, Parry, Block
RM2: Parry
RMC: Parry, Dodge.
The basic essential rules are designed around the RM2 concept, where "Parry" essentially consists of "Attacking in a defensive manner" with no other options.
RMC tactical adds in Dodge, which consists of no attempts to use your weapon for defense, and just avoiding attack.
Neither has added in the concept of "Block" as a pure action in and of itself. . .essentially, a "Full parry with no attack" is blocking, which the rules simply don't cover as is, except perhaps in the DB bonus from a shield.
Perhaps Tim will add "Block" in the combat companion. . . .