There are way too many portable filler games in the series.
By "way too many" you mean 2? Really, there aren't as many side games as people claim there to be. COM is a bridge game so it doesn't count... BBS has been said a million times that it's a main game... KH1 and KH2 are obviously main games. The Final mixes don't count as "side games" because they're just remakes. So it just leaves 358/2 Days and Coded. That's really only 2 side games.