Ah yes, another Fire Emblem argument. I really shouldn't respond but I feel this compulsion to do so. To start, I understand why people are upset with there being more Fire Emblem characters. It just boils down to not being the character(s) they wanted, and there's nothing inherently wrong with that.
1) No, Marth, Lucina, Chrom and Roy do not play the same. Their movesets are similar, but they do not play the same. It may be semantics for some, but it shows, in my humble opinion, a larger flaw of speculators in that they don't digest the gameplay aspects of the characters, or why they're designed that way. If you try playing Marth like Lucina, you're gonna have a tough match. If you try to play Roy like Marth, you're going to struggle. While the moves are the same, the way to properly play them is not.
Also, I will not take the "a casual wouldn't notice" as a valid point. Just because you're a casual player doesn't make your assessment that they're "the same" correct. It's incorrect.
Lastly, if you seriously think Ike plays like any of the 4 I already mentioned, then I find it quite hard to believe you're arguing in good faith. Having the same weapon doesn't suddenly mean you play the same way. That's extremely faulty logic.
2) Is having the protagonist of each Fire Emblem game that has a playable character in Smash "bad representation"? Depends on how you look at it. Considering Smash is a mascot crossover, you wouldn't randomly pick a lesser known character who uses a unique weapon, as they aren't a mascot or protagonist. That more or less goes without saying. Sandwiching several weapons together doesn't always create a "great" or even "functional" moveset. Similar to when people suggest Mario gets a bunch of different things to "better represent him", there's a lack of moveset philosophy involved. How does the player earn KO's as this character? What archetype are they? Mashing things together isn't good moveset design, though it can be depending on the archetype. This is why, in my humble opinion, it works with Byleth, but won't work with everybody.
Does having Ike use several weapons represent him well? Or using his signature weapon from his games that works in a functional moveset?
So, does the blame lie with Sakurai or Intelligent Systems for each of the Fire Emblem using swords? Sakurai doesn't have control over the Fire Emblem series, so it seems that answer is obvious.
3) "Anime swordsman" is a non-argument because it doesn't mean anything. It applies to Fire Emblem characters, but never to Shulk, Link(s) or other sword users, or at least not consistently. It's more or less a substitute term for "character I don't like with a sword". If this weren't the case, then there'd be no fan demand for Rex...a character that comes from a JRPG with quite a few anime tropes in it, ironically. If anything, it's more based on the appearance of the fighter and the weapon they use rather than holistically how they use it...which is what already makes each sword user different from the next.
Fans need to come to terms with the fact that most gaming protagonists, if they don't use their fists or a gun, use a sword. It's the easiest weapon to translate to fans (considering it's consistently used in most media, not just video games), and one of the easier weapons to translate into gameplay.
But it's also extremely ignorant to say that any Sword Fighter wouldn't bring something new. Dante uses his sword Rebellion, yes, but he also has style switching, has a Devil Trigger meter, and has his two pistols Ebony and Ivory. Despite having a sword, he'd be nothing like the other characters. 2B would be quite similar...in that she'd be inherently different despite using the same weapon. She has a light sword AND a heavy sword, AND a bot that fires rounds from afar. This is, again, totally different from other characters.
The whole argument is silly and just reeks of people not understanding differences in gameplay, or the larger context of sword-users in media.
EDIT: I think the craziest thing with Byleth is that Sakurai went out of his way to include weapons that weren't swords in the moveset, and people are still mad.
Why are they mad? Because it was never about the swords.
It's been over a half a year that another Fire Emblem character, from one of the best titles on Switch, which made sense as a marketable title through Smash, was added. Let it go, dudes.