I agree too with the OP, and see absolutely no sense in those trying to reason the current system.
To those arguing that it 'encourages' chasing down the player:
1. In the system presented by the OP, those who get ANY damage onto the target will receive an "assist" gold bonus.
2. So it stands, that if the target is NOT chased, then no-one gets any bonus'. It can HARDLY be reasoned with any credibility at all that bringing in a new system will all of a sudden stop people chasing down a DG in-game. Practically, that is just silly.
To those arguing that it improves strategy and gold allocation opportunities:
1. It is MORE strategic to pick and plan your fights and your time investment and hence, your gold rewards. If you know that you need a gold boost, you will be prepared and take on that DG, because you KNOW that you will get the rewards, even if someone helps mop them up.
2. If by rote, you are picking the occassions when you decide to face a DG, but someone else comes along and gets the majority of the credit for it, then isn't that a counter-intuitive misallocation of resources? They certainly didn't plan to take on the DG, they just came along for the ride- your whole team is affected by this misallocation, as having 4 equally powerful DG is more effective than 1 extra powerful burst-dps killing blower.
3. So if I'm in need of a bigger gold injection, and I pick out 5 fights, and 4 of them are wasted time allocations as my damage is consisten rather than burst and it's been taken each time, that gold won't ever come back to me- my character is effectively gimped by others' item bonus'.
4. My only concern is how such a system effects the more passive classes like Sedna. I haven't had much experience with her, so I'm reluctant to comment on her, but I'm sure there must be some effective way to take into account healing and non-damage boosting skills. Perhaps she isn't as item and gold dependant as the other classes to begin with, not needing the expensive life steal and +weapon items?
And for those arguing it's a team game, the 'team game' argument works JUST as easily for the proposed system. What the proposed system DOES improve is the allocation of gold to the DG who invested the most time into it, and that's as it should be, as DG games are short and quick and time is our most important commodity to player and item levelling.