No,they definetly shouldn't go back.
The new lore isn't perfect thats true,but it is far better than what we had before.
The old lore never really went anywhere with most of its characters and a lot of the justifications for joining the league felt rather forced(oh hey Lulu,you are weird?Then join the league,a brutal bloodsport where you are forced to fight friends and foes alike and kill each other over and over again).
Not to mention that a lot of the mechanics of the league were rather inconsistent(summoners were aopearantly not forcing any champion to participate in the league,yet that is the entire background of Nocturne) and would have resolved some conflicts easily(as they showed the ability to summon the actual bodys of the champs against their will and lets be honest,here resolving every major conflict with a league match would have gotten really old really fast)