Well you're welcome to have a personal interpretation of the implications but to be 100% clear it absolutely does fall under the commonly accepted definition of mutilation which is

to injure, disfigure, or make imperfect by removing or irreparably damaging parts

I suppose if you wanted, you could argue that the benefits of the mutilation outweigh the detriments, but it definitely is mutilation.

This is different from, say, amputating a limb which presumably has already been mutilated or harmed in some other way (and is thus already imperfect and injured). But a circumcision (besides from some kind of medical necessity) is taking an already healthy part of the body and injuring/disfiguring/making it imperfect.