NOTE: My opinion only
As to the mentioned different loads. One needs to remember that the guns in question; Paradox, Explora, Jungle Gun, Shot & Ball, etc. were not all "mixed use" as in for wing shooting, small game, and larger game.

There were "Paradox" (I will use just this word to describe them all) guns made to quite different weights depending upon what the owner expected to use them for. The light weight 3 1/2 Dram ones were certainly expected to be used for wing shooting, small game, deer, etc. and developed 1000-1100 fps with typical round ball or conical.
Then there were the 12 bore guns made to weigh 11-13 lbs that were undoubtedly meant not for any wing shooting but for the largest game. This is where those mentioned heavy 7 Dram loads were used and they gave 1500+ FPS velocity to the round balls and conicals.

I have a full rifle Lyon & Lyon 12 Bore weighing 13lbs 1oz proved for 191 grains (7 Drams), later on the makers and sportsmen found that the "rifled choke" system offered equal accuracy with allegedly less recoil & greater velocity compared to the fully rifled arms.
7 Dram 12 Bores are/were not rare at the time and ARE real thumpers. The heavy 12 Bore guns seemed to be much used in India against all sorts of large game. Whether that same heavy 12 Bore was prudent against Buffalo, Gaur, or Elephant was/is subject to debate then and now.

-Mike