I'm pretty sure that S-Hancock has some other ability which might not even be related to love since Usopp was also turned into stone.
Boa's ability is about finding her attractive, but not necessarily in a sexual sense.
When York was turned to stone, she was clearly doting on S-Snake as if she was a lost child, without any sexual intention.
Attractive means you want to be around someone. S-Snake proves that Boa's Mero Mero Mellow turns you to stone if your heart is swayed by her.
Luffy wasn't attracted, because beauty/cuteness doesn't mean anything to him, Luffy invited a skeleton to join his crew immediately upon meeting him.
Oda is consistent here, just doing a bad job of explaining what's happening.