I agree. I actually try to think of the Spotpass Paralogue characters as some weird alternate "what if" scenario.
I'm still not convinced that they aren't just bonus characters.
In previous games, bonus characters (like the extra characters for bonus maps in Biding Blade and Path of Radiance, and the creature campaign characters in Sacred Stones) joined without any storyline excuse, but here even the past game DLC characters technically have story reasons for joining. They don't have unique dialogue afterwards because they're considered guest avatars by the game engine, but they do get it before and while joining. Those six characters having complete dialogue sets makes sense, considering how they are actual standard characters engine-wise and the treatment given to bonus characters in general in this game.
Besides, you need to unlock the spotpass chapters in the same place where you can get legendary weapons out of nowhere and make past game characters randomly pop up in the world map. Awakening likely won't have a direct sequel though (the pairing system makes it extremely unlikely), so I guess this discussion likely won't be settled any time soon. I think we're likely to see bonus crossover characters even more fleshed out in future FEs though, since they likely won't only think about the concept at the end of development, which at least will hurt the arguments that selectively go "If they have dialogue AFTER joining, they're canon" to support the spotpass chapters characters.