The start of the YouTube video puts the exposition of the attack from one film next to the exposition of the attack from the other. Is that really such a strong similarity? I'd guess a lot of war/action movies have a here's-how-it's-going-to-go-down scene. Some of the other pairings are closer - I think I buy the one with the line about the number of guns.
So, I see a Dam Busters reference, and that's interesting! But I'd need more convincing that it's used for storyboarding.
"As the British pilots approach the superstructure, one asks, “How many guns do you think, Trevor?”
To which Trevor replies, “I’d say there’s about ten guns. Some in the field, some on the tower!”
The similarities go even further… A tense countdown leads to the first bombing of the German dam, just like the trench run. After the first bomb attack against the German dam is away, one of the pilots exclaims, “It’s gone! We’ve done it!”
To which he’s told, “We haven’t! It’s still there!”
That bomber tells his other pilots to set up for their attack run, eventually taking three bomb runs to destroy the target."
That's almost verbatim what Lucas used for dialogue (something he always admitted he struggled with writing).
It's pretty clear that the lineage is essentially undeniable.