To correct something, Daisy has a very tiny difference by having slightly different hurtboxes. It's a worthless difference in practice, though. Every single Echo has an actual gameplay change, even if they're as simple as animations(via taunts etc.) that affect how they're hit. She's a very poorly done Echo nonetheless.
No Echo is 1:1. Those are what we call "alternate costumes" instead and don't get their own slot. The whole reason they have a slot is because they have a gameplay difference. No matter how poorly implemented it is. Richter and Daisy are two of the most ununique Echoes of all time(Dark Samus borders on this, but has electric instead of fire attacks, but is barely better. Dark Pit is next in line for a small amount of changes. Lucina and Chrom not having the sweetspot changes a fair amount of how they play, and Ken is barely an Echo to begin with, but fills the core requirements so still gets labeled one anyway. That is, same bodyshape, weight, and attributes. If he had any one of those changed, he'd fall under Clone like Dr. Mario officially is(hell, till Pyra/Mythra, he's the only one that is easy to cite as a normal Clone instead of a semi-Clone).
That said, as for cuts, in almost every case, the first character in a franchise is staying, and the only time one was considered for a cut was a special case of "rotating protagonists" with Mother. Fire Emblem never even had this thought, so Marth is 100% safe. He's the core representation, enough to get a Clone(who became a Semi-Clone later), an Echo, and by proxy another Echo to him. That's a big deal to how much they contribute as a base alone. Villager is just as safe, and the backbone for Isabelle having a moveset implemented(not that she could've have been more unique than a Semi-Clone in the first place, but she was not added to represent the core gameplay). She's really damn safe too anyway. Unless they somehow go to "1 per franchise", which is vastly unrealistic, a lot of cuts are pretty unlikely. 3rd Party stuff always can have issues(Pac-Man is normally safe as long as Bamco is part of the team, but even then he's one of the big gaming icons. Sonic is not nearly as safe as Sega actually was okay with him not returning, despite being massively buddy buddy with Nintendo, enough to have specific publishing rights to more than one game. Bayonetta is probably safe, too. Joker I'd worry the most about the three. Konami could go either way, same with Square-Enix. SNK seem pretty easy to work with right now. Steve & Alex are completely safe outside of gameplay implementation issues, and B&K are actually in the worse spot, but way easier to add in due to being far more simplistic). Capcom Co Ltd. and Capcom USA feel fairly safe to me as well. Not all the actual content, but the characters see little reason to be cut. MegaMan, Ryu, and Ken are always used, and the first two are both mascots for the companies combined.
It'd be nice if Pikmin & Alph got an Echo update, but it didn't help that Pikmin pretty much went dormant at the wrong time, and other than having the wrong personality, he does nothing unique from Pikmin & Olimar normally.