Since the amount of time and effort required to achieve a particular rank isn’t a fixed value, but instead depends on the behavior of other players, you have to consider both extremes, as well as the average behavior given collected data.
If most players only played enough to hit tier 1, and the top players only played a little bit more than that, say about 100 battles per week, would the rewards be appropriate? 11 Arcanes seems like an awful big reward for 100 battles. That would be way higher than the drop rates for challenges, or even the new Explore mode.
Now, the reality is that the top players play a lot more than that, and did even before ranked PvP and the associated leaderboard were introduced. They play 1000+ battles per week. 11 Arcanes for 1000 battles would be right around the expected drop rate of 1-2%. Before the introduction of Explore mode, even this was still a competitive return for the amount of effort.
The thing is, the developers don’t actually want to drive people to play that much:
As it is, most people will look at the rewards, look at how much they’d have to play to compete, and feel satisfied that it’s not worth their time. If those rewards increase too much, or contain something exclusive, that would really put pressure on people to compete. That would drive a lot of people either to play more than they’re comfortable with, leading them to burnout and quitting, or people determining that they’re no longer part of the target audience, and quitting. Not good for the game or the developers long-term.