Idk about an overarching plot, but in the latest episode, seeing Barbara finally fully embrace her place as a role model and motherly figure in Janine's life was up there with the most heartwarming sitcom moments I can remember. The pacing in general of the character relationships is one of the biggest strengths of this show - the dynamics seem natural and believable.
Yeah the show has definitely avoided flanderization except maybe a little with Jacob, like Ava is becoming a part of a group but still herself, Janine is able to express her feelings, Barbara is able to occasionally admit that she may be wrong etc
I think moving the school to the mall is in part because they don't want it to get stale, too. It's not that stale for me, but you don't do such a dramatic shift without something like that in the back of your mind.