Keep in mind, the landscape for character inclusion looks quite different than it did for Brawl. Back then, there were still multiple big name characters to be added, such as Wario, Diddy Kong, etc. and as much as I would've liked to see them, characters from comparatively smaller series like Golden Sun, S&P, Starfy, and Custom Robo really didn't come to the level the other characters were at by and large, I agree with Sakurai in that only Pikmin and Animal Crossing did, even if it was disappointing. This time around, as there are only a handful of "heavy-hitting, A-list characters" left (like Ridley, Toad (who I could very easily see being omitted again), etc.), the bar is effectively lower, and the competition is a little easier for who could be seen as meriting a spot.
Plus, by that logic, keeping Brawl's standards of inclusion basically eliminates all series made this century not already represented, except perhaps the Wii/Mii one. If they were still held to Brawl's standards, not only would Isaac, Saki, and Starfy not have a chance (when in reality they all have chances), but neither would Shulk. His game didn't perform as well commercially as the first two GSs, it was about on-par with them critically, and at his peak Isaac was just as popular as Shulk is, even in Japan. It's possible one day Xenoblade might be "worthy" by Brawl's standards, but it's not now. You have to admit getting at least one of these four characters is probable, even if you believe two or three are horribly unlikely.
Like I said, the bar is lower, and all these characters have varying chances. I'm not trying to say they are A-list material, I'm not even trying to say their chances are good, I'm just saying they do indeed have a chance.
Or you could keep your Brawl-era mentality, but know that it also pretty effectively applies to all series made post-2000, excluding Pikmin, AC, Nintendogs, and probably Wii, not just Golden Sun.