I like those ideas,

however Dark Samus needs reduced knockback more than reduced damage. Okay, so I have been thinking about a new entry. An entry kinda like the one Dark Samus uses when she corrupts the hunters who are about to destroy the levithan incoming to Norion in (Mp3 of course).
I have also thinking about a brand new Side-B, how about Nukes Morph ball flyer thingy. (But with more lag and can't be spammed!! And reduced damage and knockback!!) Nukes final smash animation would look great but without the arm cannon zero lazer circle thingy.

And about the animation walk slow, how about Dark Samus actually walks like she does in Mp2 before the first battle which is in Agon pirate facility!!!
About the Down-B, yeah, it's pretty spammy. How about coding like, "Shadow Lord of Chaos's" in which the Down-B only works if the person reflects at the right time or the enemy is right next to them. Those two ideas are based off all the Dark Samus battles!!! Up-B air needs to be rid of that annoying fall or just make the fall much, much smaller!! I now realize that the final smash should be like Lucario's!!! I think that was a great idea to think of something like that!!! I might actually be able to assist you with the animation since I am learning how to animate right now!!!