But note the terrible bend in the back of the second photo compared to the first. Look how open the chest on the upper rider is and how relaxed. Be that as it may, the arm position on the second rider is faster because there's less arm exposed to the wind. OTOH it's not as relaxed and harder to hold. The first rider can hold that position all day. That added flexibility and more comfortable position are relatively recent innovations which are definitely faster. I should point out that the camera is tilted a lot in the first photo. His back is actually a long way from horizontal.

However . . . the huge saddle to bar drop in the first photo depends on the rider's geometry and to a lesser extent to the bike's geometry. The position depends on it being a very long legged rider on a bike with a very short headtube. I ride slammed -17° stems on all my bikes. My drop varies from 1.5" to 4" depending on headtube length and stem. Even in the drops with my chin on the stem, my back is not horizontal, nor would the back of the second rider if he were flexible enough to straighten his back. His back is not horizontal, he's just hunched. A contributing factor to that poor position is probably a much too short top tube which was fashionable in the day, possibly because the light steel frames were so flexible.