Here is another way to look at the data:
| Players in Game | Party Damage (Assumes each player is 1X) | Monster HP | Total Drop Chance | Average Drops per player | Average drops per player per party damage/monster hp |
|---|---|---|---|---|---|
| 1 | 1 | 1 | 0.25 | 0.25 | 0.25 |
| 2 | 2 | 1.5 | 0.438 | 0.219 | 0.292 |
| 3 | 3 | 2 | 0.578 | 0.192666667 | 0.289 |
| 4 | 4 | 2.5 | 0.684 | 0.171 | 0.2736 |
| 5 | 5 | 3 | 0.763 | 0.1526 | 0.254333333 |
| 6 | 6 | 3.5 | 0.822 | 0.137 | 0.234857143 |
| 7 | 7 | 4 | 0.867 | 0.123857143 | 0.21675 |
| 8 | 8 | 4.5 | 0.9 | 0.1125 | 0.2 |
The first thing you notice is that the difference between single and multiplayer is much less than what you presented. Moreover, there is a sweet spot of 2-3 players in game assuming each player contributes 1X damage and working together. It is only after there is more than 5 players in game, that single player is more efficient.
Things look different when one player can carry the entire group.