That said, anyone with training will always beat anyone without.
This, unfortunately, is not true.
An expertly trained person can mitigate a lot of disadvantages but not all.
Devil isn't described as an International level MMA fighter or anything, she simply has been trained to fight locally.
She knows more than your average person certainly but not enough, imo, to offset such a huge physical disadvantage.
The MC here is a lazy untrained slob
You aren't getting it.
I know he is described as a lazy slob.
But
look
at
him.
He isn't a slob, the dude is fucking ripped. His shoulders are broad with defined muscle as are his arms and he has a defined and pronounced six pack. His legs also are thick and sturdy. There is not an ounce of fat to be seen on him, he is not at all skinny or malnourished looking.
He cannot look like this unless he trains hard.
Again, I don't care what the story says - what the story shows me is something else.
If you want me to believe that the PC is a lazy slob, show me a lazy slob. Don't show me a very strong and fit looking guy.
while both Aiko and Mel are trained and in far, far better physical shape.
The MC would be naturally stronger if both girls had never trained however they left him behind.
They're not in "far far better shape".
Aiko is equivalent.
Mel is certainly in better comparative shape, meaning that she might be as strong as him (but probably not).