Never said it didn't, that doesn't alter anything.
You're correct that the MC is the focus but the triplets supply the situation, take them out and the story is gone.
Never said I, or anyone else, doesn't care about other characters. And yes, every other char, excl. MC and the triplets could be removed from the game without any impact on the story = filler. Filler is important though or else the story will be quick and boring with limited options.
As for opinions; I like the filler so far for the most part (could do without the cop though).