The thing about early Fire Emblem, and modern Fire Emblem to some degree, is that the characters follow a formula. Like while you do get some outliers that have differences with their classes, many of them are practically the same gameplay-wise. Not just with their weapons, but in the gameplay role they play. Like you can have easy Echo Fighters of Alm, Celica, Sigurd, Seliph, Leif, Eliwood, Eirika and Alfonse.
And some of the other Lords with different weapons can still have easy Echos too, like Lyn can practically have any Myrmidon character as an alternate or Echo, Ephraim and Dimitri can Echo each other, Hector and Timeskip Edelgard can Echo each other if they don't give Edelgard any magic she can learn, Micaiah is a tougher one due to her light magic, but she could still get an Echo that focuses on similarly styled, but different magic in a sort of Ryu/Ken way(like Micaiah using Light magic and her Echo using Fire Magic that has similar attacks and hit boxes) and Claude can have an Echo of Takumi or another Bow character.
It's not so much that they aren't capable of unique movesets, but it's more that because they follow a formula that has stayed with Fire Emblem, it's just easy to make Echos out of them or for them.
