I think you're missing the point. Bows cannot store more energy than the archer's muscles put into them. It doesn't matter so much what the peak weight is as the distance you have to pull that peak weight to get to the breakover. If the limbs have stored 90 pounds of energy on a bow with a 70 pound peak draw weight, you didn't just put 70 pounds of effort into drawing it. Even though the peak draw was 20 pounds less, you did practically the same amount of work as someone shooting a 90 pound longbow.

By the same token, you are correct. When you've drawn that sonuvagun back and released it, the string will power the arrow at peak for the same distance you pulled it - minus however much you lose through inefficiencies in the bow.

If the arrow sticking in that old door was shot from a 90 pound longbow - and research has shown 90 pounds would be on the light end of the scale for an English war bow, so the actual bow that did the deed could've been heavier - then yes, you'd have a good chance to get a 1,000 grain arrow to penetrate a 3" oak plank with a bow that stored upwards of 90 pounds of energy.