I've watched people filet fish, even some of my friends, that make the first cut behind the gill plate .... in a STRAIGHT UP/DOWN LINE from the back of the fish to the belly, then take the extra effort/time to make the V cut to get that little extra section of belly meat

REALLY ?? (I say to myself) .... why would you cut a fish that way, losing a section of back meat as big as the first joint of your thumb, just to save time/effort .... then forfeit that time/effort to save a section of belly meat that's likely not any bigger than your pinkie fingernail ??

I don't normally make the V cut to get the belly meat, unless the fish is pretty good size. But I always make my first cut starting at a \ angle (on a fish facing left), from over the top of the head to the gill plate, in order to get that bigger/thicker section of back meat. Then I curve the cut downwards towards the rear of the breastplate/fins. And yes, I am filleting with an elec. knife. I just roll the blades under that back meat flap & then level the blades out to finish the cut down the side.

... cp