It's a really interesting topic, that's for sure. Can't help but throw in my opinion as well.
I think it has a lot to do with how the character was presented and how women in general are viewed in the series, and just the genre overall.
In AC, first of all we've seen Bitch-Sensei do similar stuff all the time. So when the genders flip, it isn't that big a deal. Seduction was a genuine assassination skill the class was taught, it honestly makes me happy seeing it being put to use. Kayano is an established character we all know, and she's frequently paired up with Nagisa - the pairing makes sense. Lastly, she nearly beat Koro-sensei to death and was about to die herself. She wasn't devalued or put in a shameful position - she's the most powerful person we've seen to date with the exception of Koro-sensei himself and possibly Shiro. And most importantly: NO FANSERVICE. No jiggly boobs, moaning sounds, unnecessary panty shots. God bless you author for that one.
In OP, it felt more like a bad joke. I know Franky is supposed to be a pervert, but for the most part he's been shown to be pretty respectful towards the ladies (especially when compared to Sanji). We didn't know the vacuum-lady, she was probably introduced soely for the joke and played no important part in the story at all. She was just there to show how "manly" Franky was. The whole manly gig kinda confuses me to be honest. I understand where Oda comes from, and from certain angles it is pretty hilarious, but the way it was played out both on the male and female side felt a bit awkward at times. I was fine with them using silly moves and the ladies falling in love and cheering them on, but the vacuum-lady kiss and the bra-ripping parts were too much.