League of Legends, the game, is not Summoner's Rift. League of Legends, the major esport, is Summoner's Rift.
The problem isn't that alternate maps aren't balanced for as much as SR and rarely promoted; the problem is that alternate maps are barely balanced for and almost never promoted. Despite being permanent maps alongside SR, alternate maps get nearly no developer support. The last systems update either map got was during 5.13 back in July; the last champion balance change was in 4.15 from August 2014. The only promotion any of the alternate maps has gotten in years was the Bilgewater skin for ARAM. Various League features (e.g. minion projectile clarity, Champion Mastery, brush animations, minion skins) are missing or were tremendously delayed for alternate maps.
Promoting SR as an esport is fine. Positioning SR similar to traditional sports is fine. Pretending that parts of the game itself simply don't exist is not fine.