Imagine if Gyaru mom is Mitsuki's actual mom before she left/divorced Mitsuki's dad and went to marry/date her second husband we see in the "Gyaru mama - After going out" Video. That'd be a wild twist
That could be a possibility. If we assume the same slutty and hypersexual behaviors Mitsuki ended up having came from Gyaru Mom and they manifested early in Mitsuki, then we could also propose Mitsuki was the one grooming her dad into going to her for "relief" long ago. A sort of "reverse-grooming", taking advantage of that fact her dad was lonely without Gyaru mom in the picture. It would explain why her brother, whom appeared in much earlier animations, was so nonchalant about her and her dad getting on casually in the living room as he figured there was no helping Mitsuki. Effectively having given up or gotten used to it. Kinda dark, depending on whom you ask.
In this scenario, Mitsuki was always a devious minx and she corrupted her dad. It would explain why he is also so weak to her, and why she is more than eager to do what she does without a care in the world. Of course this is nothing more than mere speculation.
But even if we settle on the simple argument of her dad being a huge perverted POS who groomed his own daughter, I don't think she is an idiot. Mitsuki knows what she is doing, she knows her circumstances aren't normal, she knows she has options, she appears to actively enjoy what she does to and for her dad. And her sexual habits mirror that of Gyaro Mom, both being pleasure-doms.