When I was 'prenti, forty years ago, I was taught to fillet medium and small fish with something like this Forschner Wide Fillet:
The one I used in the restaurant was carbon and got lost when I moved back to Los Angeles from Northern California in 1975. I bought the same stainless Forschner you see here, and still use it for all sorts of utility stuff, like opening packages, cheese, pies, etc., but almost never for prepping and never for fish.
I was converted to Japanese style fish prep many years in the nineties, which means using the same knife to cut off heads and tails as for filleting, then switching to something more delicate for portioning. So stiff and tough is the order of the day for filleting. Dave, the sushi man who taught me used a couple of rugged chef/gyuto profiles because they were cheaper and more versatile than debas. Because that's how he taught me, because I honor him, and because I'm left-handed, I do the same.
Accordingly, I'll use a TI carbon "Nogent" 7" chef's for smaller fish, or a 10" K-Sab au carbone for the big boys. My wife isn't much of a fish eater, so we seldom do larger animals. Next time one happens, I'll consider the Richmond Ultimatum which has knocked my 10" Sab out of ordinary use.
And from right to left, in the same order mentioned above, here they are:
Note that all of these knives are relatively heavy, and made from very tough alloys. I wouldn't consider using anything as light as my Konosuke gyuto (or suji).
There are a lot of really good Asian fish markets in the SGV, and almost all of the guys who work in them use butcher profile knives for cutting big fish. You see the same profile on videos of guys on Japanese fishing boats. If I did a lot of fish, I'd seriously consider investing in an Old Hickory. Stiff, gets sharp, and has a shape you can lean on.
Of course you'll want to sand down and oil the handle, and perhaps crown the spine. But what do you expect for $15?
If you want to avoid ragged fish flesh, it's more important to approach the filleting with sharpness, speed and confidence than with perfect technique. Breaking fish is one of the few skills in which taking your time is a drawback. A heavy, stiff knife you don't have to worry about is a big plus. I can see skinning and portioning fish which has already been taken off the bone with a suji, but not actual filleting. At least not with my knives, you don't.
If it seems like I'm laying down the law... No. There a lot of ways to break a fish, and any method or equipment which work for anyone else makes me clamtastically happy.