point taken, if next season is devoted to balance and reworks, whats the worse that could happen?
well i guess a few people might get bored and leave, but in the end I think more people would enjoy a more balanced, and of course future Riot programmers would appreciate a better foundation and less code spaghetti
and you gotta remember all the people who freak out when the game (in their eyes) is almost rewritten, could also apprecoate a more lax pre-season in turn for more balance
but then there are content hog as well (would this season be without new champion releases?)
what you said is what most reasonable players want, and what a lot of Riot employees may want as well. Riot is also a company that promotes a free game, they still need to make money, and that comes from expanding their viewer base.
Also remember more money can equal more capital to create a better game (balance, foundation, programming) in the future.
Maybe waiting till they are in the best financial or popularity state possible (meaning the least possible risk of losing a large amount of viewers, or money) to take a break from making new stuff to devote all their time to balance