Women tend to get the benefit of doubt that they are the better parent and that the relationship between a child and a mother is generally more important than that of a child and father.

ironically I would give this as an example of patriarchy, as precisely the kind of thing feminism aims to eliminate ...

Raising the importance of how we as a society view that relationship rather than bringing down the importance of the mothers relationship.

I think the feminist approach might be to stop thinking of children as primarily the responsibility of mothers, that both parents should be responsible and engaged, such that the courts wouldn't assume the mother is "the parent", while the father is more like a "provider" (that's the patriarchal setup - women don't earn, they stay home and serve as housekeepers and caretakers without pay or economic autonomy, under the control of the patriarch of the family who earns & controls the money).

Although that largely falls in line with my personal opinion that criminal sentencing in this country is far, far too harsh.

if you are talking about the U.S., there is a huge discussion about prison abolitionism, but I think there is significant overlap between various social justice movements, and contemporary feminism has been focused on recognizing how interconnected these struggles are (we can't just narrowly consider "women", as that often leads to only considering the experiences and rights of cis, middle and upper class, white, and able-bodied women).