And now you have! That gaunt below him looks freaked out, too.
You know how they have power gauntlets that are basically miniature powerfists and that one Blood Angel has that "Death Gauntlet" or whatever that includes a digital weapon for each knuckle? Not to mention Lucas Alexsander's wrist-mounted plasma gun. Why not give every Astartes standard-issue wrist-mounted plasma gun and wrist storm bolter. They can carry a .998 cal Bolt Gun to deal with the big stuff while using the plasma gun to take out small-ish but important groups of enemies (like Nob squads) and the storm bolter to mow down the cannon fodder. Have both wrist-mounted weapons connected to an ammo/power source on the small of the back. Give each a chainsword wreathed in a power field, too. Oh, and replace their ceramite with the stuff Achilles Land Raiders are armored with (they can shrug off meltas).
I hate that I know this but it's all part of the Dark Age perceptions prevalent in 40k universe. At least in the greater imperium. Making the very logical and tactfully sound modifications u suggested would be akin to the Machine Cult as it would be to Christians if you slapped a raging erection on the image of the crucified Christ. They're not allowed to just "make changes" to laid out building plans and designations of particular weapons and machines of war. I do like your idea. I've always thought the wrist mounted weapons need more expansion and use.