Mesae, you gave up too easily -- although in either case the lighter aircraft wins.

Lets just pose the scenario for discussion. I suggest a heavy transport aircraft -- something like a C-130, as the test case.

Two planes flying side-by side -- one fully loaded (~150,000 lb) & one empty, with min fuel (~100,000 lb), cruising @ 300 kts. Both have a Vne of 400 kts (I don't know if those #'s fit the Herc scenario, but they seem reasonable to me). This makes lots of excess power available for initial acceleration.

Green flag --- throttles to the firewall, while simultaneously pushing over.

The unladen Herc with its greater power-weight will initially out-accelerate the heavy bird, as they push over into the dive.

As the dive angle increases, additional power is added by gravity & drag becomes increasingly important. At some point the heavier aircraft has gained sufficient power from gravity that it has an advantage in power-drag. It begins to close the gap as Vne is approached by both planes -- but the heavier plane is now moving faster.

Throttles are now closed to avoid exceeding Vne & the heavier plane, moving faster, is forced to reduce the dive angle first, regardless of whether it has overtaken the lighter aircraft. Moreover, the pull-up rate will be lower for the heavier aircraft to avoid exceeding structural limits, giving the lighter aircraft an additional advantage in being able to more closely approach Vne before pulling up.

Both aircraft are now diving at Vne with throttles closed, but the lighter aircraft must dive more steeply to derive sufficient power to achieve Vne, and thus steadily increases its advantage.

No contest.