I recently serviced the BB on my 1950 Norman Rapide. The cranks are Williams, nice but not top-of-the-line. While I had the left crank arm off, I put it on a scale: it weighed seven ounces. Then I weighed a cotterless crank arm, a Shimano 105, ca 1995, very beefy looking: also seven ounces. To be fair, the Williams arm is 165 mm, the Shimano one 172.5.
IIRC, the early Shimano 105 cranks were cast aluminum instead of forged and needed that beefy look to be as strong as the slimmer looking forged ones. Out of curiosity, I weighed a forged SR 165mm crank arm and it was six ounces; so a bit lighter than the Williams cottered one above, but not by that much.