Is there an alternative to "motherfucker" that people would actually use?
The word can have swearing but not genderisation which might be offensive (mother) nor allusions to sexual dominance (motherfucker). Nor, other possibly offensive connotations. It seems that the word is commonplace and people won't stop using it, so an alternative to the word may be useful. But the problem with alternatives, is that people might not use them unless they carry a meaning that's attention grabbing in some way, and when it comes to this word it needs to be able to be used in either a serious (non-funny) or comedic way.
I think you also need to let go of the desire to be better than common culture, and/or the desire to engineer a better culture from an external perspective. People are gross and messy, imprecise and reckless. It's what makes us interesting, motherfucker.
I actually think that depending on the context asshole is more hurtful than motherfucker. "He's a stupid motherfucker" seems like you are just angry. "He's an asshole" sounds like he legit is a ln awful person. Not a dominant fucker or anything. Just a dirty, unpleasant being. It is more demeaning I would say. I would be more hurt to be called an asshole than a motherfucker.
Swearing is fine what the fuck (just demonstrating). It's more about trying to avoid offending demographics of individuals or upholding oppression/oppressive views.
I think the more "valued" or preferred part of an insult is rather its phonetic or expressive aspect rather than the semantic one. Of course the semantic parts plays a role, as well, but the need to use stressed syllables to express oneself, or simply vent out the emotion, far surpasses the need to utter a semantically-accurate syllable or word to badmouth someone or something.
It is a beautiful insult that can vent out the emotions, or can be used for fun among friends etc. that uses no semantics to insult people, but uses very mouthful words to stress and some unfocused (as in not targeting any types of people) pragmatics, like insulting someone by insulting their parents, and insulting them as such making them out to be not something they are (was an x, smelt).
So, whatever semantically gender-neutral alternative you are looking for, consider to have a very strong expressive aspect to it that sticks to tongue.
I'm good with sticking with plain old motherfucker and have absolutely zero intention of replacing it with some convoluted bullshit alternative. I figure if he/she/it/they/them are offended by my use of the word motherfucker then it's aimed at he/she/it/they/them anyway and all those motherfuckers can get fucked and stay fucked. Tired of catering to everyone's sensibilities. Grow a pair, or a twat, put on your grown up panties and get the fuck over it.
I thought OP was looking for minced oaths that could be used in its place, and this is the first thing that came to mind for me. I use this one all the time because I try not to drop the big one around my five- and three-year-olds.
I use buttfuck/buttfuckin' an awful lot as an adjective but not really as a noun. Come to think of it, I don't often -- oh, no, wait, when my cats are being unreasonable we do call them little assholes, but swearing at them turns it into a term of endearment anyway.
Dipshit, wanker, buttnugget, cunt, probably my top go-tos lol. I kind of love how some people just hate the word cunt.