Honestly, before I thought Docter Mario not being counted as an echo made absolutely perfect sense. Lucina and Dark Pit played pretty much exactly as their counterparts in Smash (yes Lucina didn't have a tipper, but spacing is still extremely important if you want to play her optimally). Docter Mario, on the other hand, couldn't be played quite as aggressively as his doppelganger because of his decreased mobility. You can see this in their tier placements - Lucy and Pitoo are very close to Marth and Pit while Doc is much farther away from Mario.
But then they showed Chrom, who without his sourspots, will probably be far more focused far more on spacing and far less on rushdown than Roy. I actually expect him to play much more like Marth or Ike than like Roy himself. And then you've got Dark Samus, who's floatier but has an actual roll and potentially more combo potential out of her dash attack.
So now I'm think the reason Doc is getting any special treatment at all is solely because he was a Melee veteran and that's it. He has seniority status, and I guess Sakurai wants to differentiate his cloning philosophies of old (reusing assets and trying to sell them as a totally different character Falcondorf style) with his new one (fun little bonus characters meant to please fans but who aren't unique or important enough to justify their own moveset).