Many people are exploiting the 'power' to drop down and gain leaderboard positions in spite of having good collection power and cards thus 'pushing down' the new players in lower leagues. In the long run, how long will they keep doing this and discourage new entries.
Also, those who invest a lot should be given more dec per ranked match than a person who invests in only one or two splinters and manages to climb up. That is more collection power - more dec. I think the upper leagues do have more dec per win but it can be set as a rule which will discourage those who exploit the system and also encourage investment.