I'm actually surprised that nobody even mentioned the fact that the Kirby franchise, Sakurai's other main series, was overly emphasized in SSE, if you think about it again. If you don't see it, here's a quick list of things in SSE that make it too much emphasis on the Kirby franchise:
1. Who's ship (other than Fox's and Falco's kinda) was a major plot element in the story? Meta Knight's Halberd. The Subspace Army uses it as transportation, it's used as a stage with a boss included, and it is used as the main carrier ship in The Great Invasion.
2. After EVERYONE became trophies, who were the only characters to be revived by DEDEDE's timers? Luigi, Ness, and KIRBY. King Dedede was also revived by Luigi and Ness as HE was the one who put the badges on them, and HE was the creator of the badges as a backup plan if everyone became trophies. Kirby, meanwhile, thought the timer that he found was food, inhaled it, and became revived later on. He was the only one playable in that level of Subspace in the first playthrough, in a similar fashion to how he was the only character in the first boss battle.
3. Other than the Halberd, the only other area from a game series outside of Smash Bros. that was used was DEDEDE'S CASTLE. It's even directly called King Dedede's Castle in-game, and its design is just like the castle in the Kirby games.
4. Meta Knight and Kirby were playable a ton of times, possibly more than all other characters, as Kirby was playable in the first few levels in the arena and with Peach/Zelda, was teamed up with Mario, Pit, Link, and Yoshi after being the one who revived the 2 that were almost snagged by Dedede, and was one of the 4 revived characters in the Subspace levels. Meta Knight, meanwhile, was playable in the levels with Marth and Ike, he was the person that saved Lucas and P.T., he was in the only pre-Subspace level with Ice Climbers, the battle against Lucario, the Halberd levels, and eventually took back his ship and piloted it in The Great Invasion, while Kirby was the one who DESTROYED the gunship in The Great Invasion with the Dragoon.
5. Dedede basically made Ness and Luigi his servants, as they helped HIM when Bowser was troubling him and Dedede even SLAPPED the Koopa King. Now that's one heck of a powerful king, by making two people his servants after only befriending them a moment ago, and slapping a GIANT EVIL FIRE BREATHING SPIKED TURTLE EMPEROR THAT ALMOST TOOK OVER THE ENTIRE GALAXY.
6. Don't forget the removed prologue, which had Dedede accidentally causing Meta Knight to lose his ship to the Subspace Army.
*WHEW* That was some list/rant. If you haven't noticed all of that stuff, by now you probably do. And one last thing, if Sakurai does make a full length adventure mode like SSE again, PLEASE I BEG OF YOU, DON'T MAKE THE KIRBY CHARACTERS THE MOST IMPORTANT CHARACTERS IN THE STORY AGAIN! THEY'VE HAD WAY MORE THAN ENOUGH SCREEN TIME IN SSE!