It's funny you have the view because when I was game theorizing this, I thought the exact opposite. Who stays powered up the longest? It's usually smaller accounts. Sure they power down some but not all. Who power down the most? Whales. Whales are either in or out. I can put a dozen examples on this very chain where when a whale power down, it's because of a investment reason, and they clean slate and move on.
Who pays the most in this system? Whales do, of course. They pay 5% just like everyone, except when they leave, they don't get that 5% back, and all the smaller accounts are sticking around benefits from their very large contribution.
A small account pays the least to enter yet stands to gain the most in the form of ROI.
It's a flat 5% that all pay and all get back if they remain in HP. If your rewards are in HP and you don't instant power down but opt for the 13 weeks, you pay nothing. I fail to see how the small count is harmed here?