There are ways to do a Mary Sue. But if you're going to do a Mary Sue, you kind of need balance. In the half I read, it felt more like she'd just pull out convenient abilities whenever.
Balancing with duality is a common way to get around the Mary Sue/Gary Stu character model. Balancing abilities with equal suffering is another way (eg. magical abilities with witch hunts, defiance of gender roles with discrimination, kindness with gullibility).
It's not the worst thing ever. Just generic. I'm binging these kinds of stories right now, I've seen these exact characters so many times and they weren't even good the first time.
Perfect characters are booooooring.
I started with Beware of the Villainess though so my standards are starting high.
Art is beautiful though, I agree.

This is a very generic-type story. The characters aren't characters. They're stereotypes taken out of a million other manga.
The protagonist is a Mary Sue. She's also painted as a strong female lead but all she thinks about is the designated love interest. She has many strong abilities (in true Mary Sue fashion) but doesn't utilize them effectively. As being both capable with a gun and apparently having high intellectual skills, she is all over the place and none of her skills shine. And heaven forbid we give the lady a gun to defend herself when she shows herself to be capable, get into trouble, and that the guns in this universe are perfectly wearable. That might show that she might be able to *gasp* survive without a man or *bigger gasp* that the love interest sees her strength and wants to empower her instead of keep her under his control! Can't have that!
There is nothing here today that you won't forget tomorrow. Terrible writing in both skill and creativity.
Ch 62 was when I reached my limit. But I was really dragging myself through it by that point.