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.