Diem
Agent of Phaaze
Actually it makes more sense that Sakurai alone picked the Fire Emblem characters instead of Nintendo.I didn't say for certainty that it was added in for that very reason. Just that it probably was, or at least could have been considering the timing. I really don't think they give Sakurai as much freedom as some people think. It's funny to imagine he picked all of the Fire Emblem characters on his own without any suggestions or any input from Nintendo for the memes, but it makes too much sense when you see how much Fire Emblem has been promoted since Awakening. Why else is Corrin in Smash before his game even releases worldwide, but Rex from XB2 isn't despite Sakurai himself wanting him in? Awakening sold extremely well and XBX didn't. On another note, Brawl was pretty much what Sakurai wanted Smash to be. A great casual game that didn't encourage people to play it competitively, but now two entries afterwards, Smash games are being made to be played much more competitively than Brawl.
If Nintendo were calling the shots and looking at things from a more objective, business point of view, why would they put so many chips on Fire Emblem, a series that, while enjoying newfound success, isn't nearly as popular as many of their other franchises in the game? Why would Fire Emblem get way more content than Donkey Kong, which is one of Nintendo's more historic and best-selling franchises? Why not add more Pokémon instead of Fire Emblem characters, since Pokémon is their most profitable franchise? Why add so much Kid Icarus content when the series was totally dead until the 3DS game, which even then didn't sell more than 1.5 million units? Or why would there be weird characters with limited popularity like Little Mac, Wii Fit Trainer, Duck Hunt, R.O.B., etc. etc.? Why not fill the roster with characters that are more recognizable and recent?
Awakening's success wasn't necessarily groundbreaking. It sold maybe 2 million units. That's a lot, but not staggering, and definitely not worth three characters and a promo character for the next game. But Sakurai's always liked Fire Emblem--that's why Marth and Roy were in Melee, after all, back when the series wasn't even really known in the West--so that was only fueled by the series' resurgence with Awakening. Kid Icarus content, especially in Smash 4, was also clearly due to Sakurai directing Uprising, rather than a business decision based in the game's popularity.
Corrin's game was released in Japan long before it was released internationally; the game was finished and out in Japan by the time they started work on the DLC. The project plan for Ultimate, though, was put together in December 2015, long before Xenoblade Chronicles 2 was even announced.
Brawl's "casual" nature was due to the Wii's target demographic being casual. Sakurai slowed down to accommodate for that, whereas the Gamecube targeted a hardcore audience. Smash 4 was made faster after it was evident that the Smash fanbase enjoyed Melee's speed more than Brawl, but not too fast because it was on the 3DS as well, and if the game was too fast, it'd be hard to keep track of what was going on. The Switch is going back to targeting hardcore gamers, and so Ultimate is reflecting that.