I don't know what you think you're saying, but to clarify:
Ravenwing Advance-and-Shoot with -1 to hit. The same penalty as if they had Assault weapons. During Devastator Doctrine.
When Ravenwing units Advance, they gain a 4+ Invulnerable vs. Ranged Attacks.
So, would you take the -1 to hit (knowing that negs to hit don't stack, so BS4 is the worst you're going to be), for a 4+ Invulnerable? On a unit with T5 and 3 Wounds?
Yes.
Would you take the -1 to hit, giving your Ravenwing Talonmaster a 4+ Invulnerable vs. Eradicators?
Yes.
It's not that Ravenwing Advance-and-Shoot without penalty:
They can Advance-and-Shoot with -1 to hit. With any weapon (e.g; Heavy and Rapid Fire weapons). During Devastator Doctrine (i.e; Turn 1, the best turn).
And they gain a 4+ Invulnerable when they Advance.
Dark Angels really want to go first, because they have a decent bonus on Turn 1 - as any Space Marine army does - but, if they go first, they actually have a legitimate real bonus vs. their opponent's Turn 1 Shooting phase (i.e; The 4+ Invulnerable).
Ravenwing are incredibly strong when they go first. On top of the usual benefits when they go first.
inb4; "First Turn Advantage isn't really an advantage."