I firmly believe that in the Slash16 dynamic, Hex is wayyy kinkier than Slasher is. Most of the robots Hex knows are asexual so he's probably pent up as hell and Slasher was literally made as a murder weapon. I don't think he's even been in a relationship with anyone and experiences very little horniness outside of him and Hex.
And on that note Slasher is definitely a sub. Like yes he's big and scary and yes he murders people but when he's making out with Hex sitting in his lap and he tilts up Slashers monitor ever so slightly to deepen their electric kiss, Slasher would do anything Hex says in that moment. He is absolutely whipped for Hex in such an earnest and loving way and he just wants to let Hex be in control and make him feel good in the way only he can make him.
And on that note Hex is definitely a switch, but when Slasher is under him just begging for another touch and so greedily trying to grind on him, Hex can't help but give the poor thing what he wants and treat him like the good little pet he is. He's very kind and loving about it and offers nothing but praise to Slasher, but he is a very good dom. He knows all the ways he can make Slasher squirm and with every little moan and whimper he makes it only fuels Hex more, until Slasher is nothing but a pathetic whining mess in Hex's claws.