I don't think she deserves her own tier but I can't see how she's better than Zelda. I've seen ChozoX and Jonny Westside, the two top samus'. They show that she can be good but again what character can't. I just think that she doesn't have enough tools to cover up her MANY weaknesses and flaws.
I don't think ChozoX demonstrates Samus well or is really a top Samus when compared with KayJay, AfroSmash, Xyro, maybe Esam. Most of the top Samuses right now are European, so we get bad rep at nationals for sure. Anyway
When I play as Samus the only glaring flaws I encounter are a bad grab, a bad jab, and poor landing options. These are MAJOR flaws (enough to make her low tier), but I honestly believe she has things that make up for the other flaws people always list.
For instance, as Zeldas, you all are accustomed to being very close to your opponent before using dash attack. If you try to do this with Samus, it will whiff and you will think dash attack is a bad move. It isn't; it's actually pretty good. It crosses up shields and is a huge combo starter. And I promise you if you learn the hitbox placement it will never whiff.
Edit: As far as Samus being better than Zelda, idk. I play both characters and they are so different that I don't think they can really be compared. I don't think Zelda is the worst, I don't think Samus is the worst... I said earlier I though tSamus was better but I'm not so sure now that I've thought more about it. Samus is more relevant as a whole competitively IMO, though, because she is a counterpick for a Luigi and Ness and doesn't have horrible MUs except for Sheik, Pikachu, Fox, and MK. Zelda isn't really a strong counterpick, though she also doesn't have horrible MUs. so IDK, overall I don't think one is noticeably better than the other.