It can be considered a subcategory yes, though it's more of a separate category with overlap.
But earlier you were claiming that if it weren't that subcategory, it's not the supercategory. That's like saying it's not straight porn if the girl isn't blonde. Completely nonsensical.
Femdom can very much involve clearly visible consent from both parties. It only requires the female to be in control. It doesn't matter if you like it, it'll happen anyway, but by god if all of us here wouldn't be lining up and like it if given the chance.
Oh, I see your point and I mean... yes, maybe I didn't use the correct words and I screw up the correct definition to explain what I want to say.
Still, whatever the correct tag would be (femdom/forced ejaculation/rape ?!) what I want to say about howl 's clips is that IMO one of the characteristics that make them so unique and unmistakable is the combination given by the frantic interaction between the strong female character and the weaker male, the struggle between them, all the little movments, contractions and spasms that Howl master to recreate and would't involved into a less drammatic interplay, as a situation where the male would act or cooperate more willingly.
Also... if you put out all the struggle elements from howl's clips what you get isn't basicanly just a regular blowjob/masturbation animaton as you can find everywhere on the net?