I don't really think it's the smartest option to use just a sword during training against Leonidas but I assume there's something that explains why behind all this

I am very confused by why Gudako is holding the sword with his left-hand. I though south paws were extremely rare in fencing.

FRien said:

I am very confused by why Gudako is holding the sword with his left-hand. I though south paws were extremely rare in fencing.

Probably the artist's choice to show Gudao first attempt at that kind of training.

FRien said:

I am very confused by why Gudako is holding the sword with his left-hand. I though south paws were extremely rare in fencing.

I highly doubt the artist is aware of the most basics of fencing or other sword fighting.

CitrusC said:

I highly doubt the artist is aware of the most basics of fencing or other sword fighting.

Honestly, I doubt it. I don't draw really well, but even when you draw stick figures, you tend to go for something that feels real (emphasis on "feels", because a lot of pictures don't actually work).
But I do have a theory : I think it's an artistic license to allow Gudao to face the viewer. If he was right-handed and swinging , it'd be harder for him to smile at Morgan.