This is why these kind of smart-contract based games didnt already gain some traction or attention due to ponzi-type similar scheme.We have seen on how FOMO3D
did in the past and it turns out to be a loss of money for most users of it.Just check out this killfish thing and this isnt really different at all and having some 5% is paid as game administration fee seem too much for me.
Of course, players who do not watch their fish will lose money, and those who care about their investment will earn, there is not any magic and money out of thin air. 5% is the usual commission for such games.