Well, the whole issue are the howker/cutter/sloop tails that make things less charming. With the 2 changes proposed, a fleet of 4 LMM and a lvl 3 howker tail will yield at maximum (with owner at 5M hand):
67.5k (74,25k with Advanced Piracy)
Min is 62.5k (no sink chance plunder)
Current System max is: 250k
Average: 151k
Min: 51k
However, if we want to be realistic, this player will most probably run on a 1M hand at most. Which means that with current system the metrics are:
Max: 51k
Avg: 31k
Min: 11k
Still, the gap at current system is considerable.
With the 2 changes proposed, the attacker will know more or less what he will get (standard gold coin plunder and a chance of sink plunder for extra gold).
For a 1M hand, the proposed system payout will be 23k min and 28k max. However, we want to believe that players will start running at higher hands for the increased protection.
Whatever we might do, the howker/sloop/cutter strategy is always going to win economically-wise. So, this is not our objective here. In contrary, we want to maintain this strategy but also allow more. It is kind of sad to see a specific strategy to be so widely used. This is the fault of the current system; it does not allow great diversity.
Sure, specialization will help more but before it can help more, some balance to the plunder system, like this one, would help.