lol I've never thought about the game like that, but that's definitely a good description of it.
Personally, I bought the 3DS for the Pokemon games, Persona Q, and KH3D. Also, if you think KH3D is a filler, just because it's on a handheld, you're gonna be confused as fuck for KHIII. MULTIPLE important things happen in KH3D (that I'm not going to ruin for you), unlike 358/2 Days which was just about the only filler in the series. Coded was almost entirely filler, aside from some mildly important details like the message Mickey wrote to Sora, Riku, and Kairi, and what happened to all of the cool shit Jimminey wrote down during the first KH and CoM. Apparently, even KHX isn't filler (which I'm STILL pissed about), because the guild leaders have something to do with KHIII
tl;dr: KH3D is fun AND important