To be fair, I don't care for customs as Mario and Rosalina (or even Shulk), but I do care for them as Samus as it patches up how terrible her specials are. That said, Samus is fun regardless of customs and they definitely do not make her some high/top tier character, yet I'd play her either way, so meh.
What people don't realize is customs make the top/high tiers even better. Mario becomes top tier, Customs Sheik is a monster, Rosalina is rofl-wow, Luigi's zoning becomes amazing, Sonic's spin dashes, the most complained about specials from viewers, become better, and Fox gets better kill set-ups.
The only high/top tiers that get no/mild benefits are Diddy(but he gets another kill option), ZSS(tumbleweed), and Yoshi(he probably drops a few spaces honestly).
Only Paluntena and DK invades the high tier picks, and I suspect for DK this is only temporary.