Rocket Slime might be..interesting...but he lacks that real Iconic Status that every other 3rd Party character has. Every gamer knows who Sonic, Mega Man, Pac-Man, Ryu, Cloud, and Snake are..most gamers can recognize Slime from Dragon Quest..but not every Slime and, honestly, Slime itself would be extremely difficult to make a moveset for and Cloud is more popular..and they wouldn't pick Rocket Slime over Slime itself.
Also, Cloud is only 'not interesting' in your opinion..other people think differently.
We have 5 pure Swordsman (Marth, Ike, Lucina, Roy, Mii Swordfighter), 4 that use other items (Link, Toon Link, Pit, Dark Pit), and 1 that also uses magic (Robin). That's only 10..11 now with Cloud. 11/56 isn't that much..we have a lot more unarmed fighters..should we stop having unarmed fighters too due to that?
If a character works and is beloved, I don't care how they fight..a weapon is just a weapon, its all about how they use it.
You may not be a 'fanboy', but I think you are being an entitled little brat that doesn't care about the fact that other people are happy and can just ignore that which you hate.
I hate Bowser Jr, I hate having him appear in games, but I don't want him removed from this nor future games since I know he has a lot of fans..and to a lesser extent I don't like Mr. Game & Watch, ROB, and Ice Climbers..but they still have their place in Smash..and now, so does Cloud. Like him or not, think he's overrated or not, he's still an Icon for Square-Enix, RPGs, and Gaming in General. He's earned his place.