Typing is mostly just a superficial particle effect in Smash though. I don't see Jigglypuff rocking that Fairy type very well or Ivysaur relying on poisoning his enemies.
F-Zero and Mother are dead series. Anything for F-Zero has to be made up from scratch as the characters do nothing except race, they're basically avatars for cars. If Sakurai couldn't get more creative with Starfox with more to work with, I highly doubt he can pull much out for F-Zero besides Captain Ganondorf turned Black Shadow.
Which is what F-Zero fans are perfectly fine with when it comes to Black Shadow. They just want a 2nd character who would fit the heros vs villains archetype that Ultimate seems to be going for.
Mother has supplied us with two kids who look similar and attack similar. It has more potential than that, but I mostly see people rally for Ninten (so 3 kids looking the same and behaving the same overall) which isn't promising.
The reason Ninten is supported is because Echos are so easy to produce and would not cost much in labor costs and resources. It would easily fit the newcomers for the trilogy of the series. (You could also argue that Duster is supported for a new take on a moveset as well, but Ninten is more prominent since he would complete the protagonist representation of each game in the series)
Not sure why you feel Starfox needs a 4th now, I'd like to see the series survive but it's teetering on failing/dying off and supplied us with 3 characters based on one kit. Krystal came into the series when it went down and Slippy is hated by most fans even though he is technically more deserving than blue fox girl that brought the drama stories along. Metroid just got 2 newcomers and it's cast is mostly one offs that play little roles and die off. Sylux could be potential, but that hasn't played out yet. Everyone else is basically dead and buried.
The Metroid part is right, but many would love to have Krystal bring her own original moveset that no other Star Fox character has.
Pokemon, Kirby, Mario, Fire Emblem and the like do deserve more characters cause they are actually successful and ongoing series with diverse casts. They are keeping Nintendo alive and what are what most people can recognize as Nintendo All Stars.
The issue is that Smash Brothers has multiple franchises that spans the entirety of Nintendo's history. To have the roster mainly support Pokemon, Kirby, Mario and Fire Emblem characters is a disservice to the vast pool of franchises that exists in Nintendo's family and library.
Trying to tear them down does nothing to help dead series characters like Isaac/Saki or one offs like Geno/Skull Kid.
How do you think they are "getting torn down"? Do you believe the general Smash fan base wants the roster to mainly consist of Pokemon, Fire Emblem and Mario characters? Smash is a great way for Nintendo to introduce/reintroduce long forgotten franchises and breathe life back into old franchises.
You cannot tear down Pokemon, Kirby, Mario and Fire Emblem because not getting new characters would not effect their series at all; whereas, series like Golden Sun would benefit immensely from Smash recognition. Fire Emblem needed that boost to kick off in the States.
There's also part of me that is pondering if they are thinking of a reboot after this already. They may slaughter the cast after this and what's the point of adding small characters like retros or one offs when they'd be the first ones cut in the reboot? Daisy, Chrom, and Dark Samus may all be old news by the reboot and could easily be scrapped or put as very low priority. Meanwhile King K Rool, Ridley, and Isabelle could be argued as faces of their series that are still ongoing and alive. All three of them could survive a reboot. Simon/Richter... have the potential as well if 3rd parties stay or are heavily pushed going forward.
The Reboot Cast depends on what the goal of the Reboot itself is. Is it about Nintendo's history and the franchises it picked up over the years? Well there goes the majority of the Fire Emblem, Pokemon, Kirby and Mario casts; especially, if the roster space is extremely limited. If you need one character to represent each franchise that Nintendo owns then you can bet that big Nintendo series like Mario would be severely neutered in size.