If I saw this picture without a name for the beastie I'd think "that's a cool variant iron golem".
It just doesn't feel like a living, breathing creature to me. I think it's the way the face seems to be part of the helmet.
Well at least the dreadnaught doesn't have dinky little legs with fragile-looking ankles like the fire giant illustration in the 5E
Monster Manual.
Concept wise I guess it'd depend on what sort of game I was running at the time. For a more outré adventure it'd be fine but I tend to prefer more grounded scenarios.
Most likely I'd mod it so the dreadnaught has a single oversized shield plus some auxiliary weapon so it's a bit more versatile (long-handled axe? spear? quiver of darts? box of rocks?).
Then again, maybe it
does carry auxiliary weapons - that waist belt presumably supports something.
Probably less than what it has, but I guarantee that question was never asked. From the drawing, each shield weighs about 8000lb. Heavy load for a fire giant is something like 5000lb. It's carrying two shields AND wearing thick bulky armor. Forget realism. Under the game rules, that giant ought not be able to even budge itself from its place, and would require aid just to free itself from the prison of armor its been placed in.
Hmm, fire giants are 18-footers in 5E I believe, so let's see...
Two shields each about 18' by 6', approximate them as being, say, 1-inch thick steel. That's a total of 9 cubic feet of steel and steel has a density of 7.8-8.0 or so which comes to around 4,500 pounds per shield.
I guess they could weight 8,000 apiece if they were thicker metal, but I'd assume they'd be made of something considerably lighter faced with metal since, well, that's how shields are made. Presumable something fireproof (red dragon bone? wood from fire elemental trees?).
A real-world tower shield is what, 30 to 50 pounds? Scale that up by the cube of 3 and you get somewhere around 1,000 pounds a shield. That seems more practical weightwise but doesn't match the visual very well.