Until we have the game in our hands, there's no telling what the differences are. Even with gameplay footage, that stuff is all liable to be changed by release, especially little tweaks to something like a character's weight. As far as I'm concerned, no Echo Fighter has ever had their weight properties changed, because that's one of the most important elements of a character's balance, and Echo Fighters are supposed to be easy to make and balance alongside their template character. But we don't really know, because Smash Ultimate Echo Fighters are a different caliber compared to Dark Pit and Lucina, who were last-minute additions that are basically alt costumes, as opposed to Dark Samus, Daisy, Chrom, and Richter, who were all planned from the get-go and have much more work put into them.
A lot of conceptions about Echo Fighters were shattered in last week's Direct. We thought they had to have basically the same animations, but Dark Samus disproved that hard. We thought they had to have the same exact moves, but Chrom cleared that up. Some people thought that newcomers and third parties wouldn't have Echo Fighters, but Richter surprised everyone.
Echo Fighter doesn't seem to be as hard of a term as we were led to believe. It seems to be a looser definition of characters who are between clones and alt costumes, but their complexity can vary. There's probably still two or three more Echo Fighters left to be revealed, so I'm sure in a couple of months our conceptions will be changed once again.
So it's possible that Dark Samus will be floatier than Samus, but we can't know for sure. I'm going to spend a lot of time analyzing this stuff on December 7, that's all I know.
Well, there's no reason you can't have both kinds of Federation in any given game. Most of them imply it's only certain parts of it that are shady, and their interest in Metroids is more along the lines of their practical applications rather than use as biological weapons (only the rogue faction in Other M displayed that interest). Fusion's ending, I feel, is hopeful enough that there's enough good people in Federation that she'll be vindicated for what she did on the B.S.L, even if there's also some bitterness in the trust between the two being shaken.
The reason we see more of the bad parts of the Federation in the later chronological entries probably has to do with a lack of Pirates threatening to steal and use Metroids and other tools against them. Even those dubious members likely agreed it was better to destroy them entirely rather than risk Pirates having them.
It's totally possible that there's two sides to the Federation, and that's the cause of that discrepancy. That would actually be better writing, to have there naturally be good and bad about such a large organization, as having them just be one or the other would be rather shallow and one-dimensional.
The problem is just that, so far, it hasn't been handled well. That's because Retro out in Texas did their own thing, and Sakamoto over in Japan does his own thing. Retro's version makes more sense in-universe, since Samus is a valuable ally to the Federation and it would make sense that they respect her for all she's done for them. Sakamoto's version is more or less a ripoff of ideas from Alien, the franchise that initially inspired much of Metroid. Except now there's no reason to continue borrowing from Alien because Metroid has grown into its own thing and should be able to use its own ideas.
Other M states that, despite taking place after Super Metroid, which is after the Prime series, it's Samus's first mission with the Federation on her own. This led some people to believe that the Prime games weren't canon, but in truth it's just a continuity error because Sakamoto has his own vision for Metroid and Samus, and it's not what we get in the Prime games, despite the Prime games being most people's favorite interpretation of things. This illustrates that the discrepancy in the Federation's representation has more to do with the different developers ignoring the other games and less about these things being planned intelligently. Sakamoto wasn't thinking at all about Admiral Dane when he was writing Other M. Thankfully Other M has been widely acknowledged as being a mess and contrary to almost all established depictions of Samus and the universe, and Samus Returns and Metroid Prime 4 are putting the series back on the right track.
I haven't fully played through Fusion yet, though I plan to do so soon, but it seems like it leaves the series in a bad place story-wise. Not sure how well the story of the next chronological game would be if Other M is any indication of how a larger "The Federation is shady and evil and out to get Samus" story were to be the focus. It could be executed well, but it would require a great deal of craft that most Nintendo games in general don't bother with. They'd need people who really know what they're doing to carry the Metroid franchise forward.
