To be fair I don't have a huge knowledge on game balance so I'm not sure how well it could work, but for F-tilt I would personnaly give her a short range beam shot which could help more for spacing (this would be similar in a way to Mii gunner F-tilt). Now that I'm thinking about it, I think down Smash is fine in theory, it's just way too weak (although it is very fast). It's good for edgeguard, but it rarely kill.
I think that Power bomb is a great idea for a down B. This make me think of Smash 4 custom moves
Mega bomb. They detonate after 3 seconds, and you can only put one on the stage at the time, but they're way more powerful. Again, it would probably need some balance, but I think this would be better that what she have right now.
Finally, the Jab I would change it for just one hit instead of a combo (this would be similar to Ganondorf neutral attack). It would be way faster than Ganondorf's, but would be weaker. Last thing I might change would be the F-smash. To be fair this one doesn't really need to change, but I think it could be interesting to give her a long range attack as a Smash like Mega man or Mii gunner. I think something that could work would be the wave beam from Metroid zero mission (the gif is how it looks in game), but there would be a lot of other possibility for a projectile smash. F-smash is pretty fine as it is, but I think that giving her a long range Smash would really help her to focus more on zoning. Right now F-smash is pretty weak unless you hit with the fiery part, so giving her something that have more chance to hit would help her. Again, I'm not sure if it would be balance, but I think it is something that would be worth exploring.
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I think all those changes would make Samus more true to her franchise. She would have less melee attacks, and could focus more on staying at range. Her attacks could have more lag so she's not too powerful. Down Smash would be a better killing moves at close range, but she could also kill at longer range with F-smash (assuming this isn't borken). Finally, this is more nitpicky, but I would change her design for the suit in Metroid: Samus returns instead of Other M.