I don't think only letting the top 10-20 would be the best option, especially 10. It kind of locks certain features of the game from current C2P & F2P players who were smart enough to invest their resources to acquire a high ranking. Although the option to get more coupons without spending ingots would be a great idea. Top 50 should allow for a decent amount of servers to have all three types of players at the top. How to balance the plunder? Ask a game designer.

It's true that those who are smart or those who pay should be rewarded for their efforts, but you can't have a game like this without throwing a bone to the C2P & F2P people playing because the game kind of needs them to be brutally destroyed by whales to keep the whales happy so they'll continue paying more. If everyone but the whales are neglected, then the whales gonna quit because whales won't be happy fighting other whales who have whaled more. Gotta think about the money, because money makes the world go round.