The payout stands in no relation to the time commitment you have to make to progress in the league. You'd have to return to the game every few hours every day of the week and have a high enough level, equipment and purchased plenty of stats to even have a slight chance of rising to higher leagues. And except for the very last leagues, the koban and cash payouts for most placements are lower than solving all daily quests and fighting Roko-sensei 20 times.

Add to this the fact that the game gives me the dreaded "HH_1 error" with a more than 50% chance whenever I start any fight in the game and you can figure that expecting me to do several hundred battles whenever possible to rank up is just impossible.