I think that people are adjusting to their abilities and you can't fault them for a strategy that allows them to at least be competitive once in a while. rather than watching the strongest take the prizes week after week. They have wisely chosen to alternate the amount they participate in the Brawl. This allows for those that don't have the will to do a brawl every week also to take a rest.  These Yo yo Leagues as you have Labeled them seem to realize better to have some rewards  sometimes than to constantly be in the 11 th place and higher spot and watching the bigger leagues score placement sapphires. I doubt the game will change the mechanics of this  feature. 

But you never know . 

 I personally think the brawl is very fairly done and that these leagues are doing what they need to maximise their leagues potential.

Leagues cannot always score massive points every week - some people get busy with life from one week to the next and don't have time to invest EVERY weekend for brawls

Agree with you ,for sure the players have a life , but  consider that you can stay down 1 week and the next brawl you can fight with all your forces at 100% and earn more points or win some place in top 10  !