In my honest opinion, Samus could move to the bottom of mid tier if Meta Knight was banned. The reason being she has the tools to circumvent the other top tiers broken stuff whereas Meta Knight is a mass of cheapness altogether. Let me break it down:
Snake: Grenade drops, ftilt, and utilt are much less effective against Samus due to her being able to fight out of close range for the most part and dair to Snake up-B is very good.
DDD: She has it easier than the other infiniteies due to being able to both projectile camp DDD and space against him. Plus he is a big target for zair and he does not have the tools to conviently get past her missles outside of simply shielding them. Provided it is still a 30:70 disadvantage, but Mario and Luigi would kill for that matchup.
Falco: Depends on the stage; it is imo even on Lylat and Battlefield, but she gets wrecked on Smashville and Final Destination. Falco does not completely destroy her chances of viability though.
G&W: 60:40 or 65:35 advantage against Samus. His bair is less effective in this matchup since her zair beats it; also note that he has to jump in order to pull it off. Now from my matchup experience, he cannot approach from long distances because she will see it coming. He needs to be in mid range in order for bair to be more effective. Samus just needs to keep him out of that space, and her ftilt is good at doing just that. G&W has the advantage just through his sheer kill power advantage.
ROB:Don't have too much experience in the matchup, but I am pretty sure that ROB does not wreck her if not an even matchup.
Samus's placement in a tier list without Meta Knight will probably depend on the success on the high tier. The members of the high tier just have unorthodox styles/abilities that force the Samus to rethink her strategy (Lucario getting stronger, not being to camp Pit at all, combating Wario's superior close combat game AND spacing ability, Marth and Olimar's existance, etc.). If the high tiers become far more commonplace, Samus will have no chance for mid tier.