The power armor we have doesn't have a power generator, which is the first flaw in your plan. It basically runs of a stored battery, and isn't designed to be hooked up to any sort of weapons - power fists being an exception, since they and power armor both run off a backpack-mounted battery. Weapons have their own internal power cells and ammo supplies, and being armored does not increase your strength nearly as much as might think it does; a moderately strong man with Strength bonus of 4 can carry 18kg easily - power armor adds +2 to your Strength bonus, and it scales linearly at +9kg/point until very high on the chart, so he can instead carry 36kg without penalty. A Man-Portable Lascannon weighs 55kg, so you'd need the armor simply to be able to lift the gun off the ground. Space Marines tote heavy weapons around not from their armor, but because of the massive skeletal and muscular reinforcements the creation process gives them.<br/><br/>You'd be limited to 1d5 hours of operation, you'll be hulking and slow (especially if you're toting that lascannon), which<em>will</em>get you killed. Power Armor only gives you 2 Armor Points over Carapace armor, giving you a likely max soak of 12 or 13. A Boltgun will do, on average, 12 points of damage while simultaneously negating 4 armor points, so you'll take 4 damage per hit from a 2-3-hit salvo, and you only have maybe 15 HP.<br/><br/>As for imagery...yeah - the part you're missing is the<em>being a Space Marine </em>bit. Power Armor is their realm because they have the sheer bulk to carry it effortlessly, and also because their power armor is far, far better than ours. They don't show ordinary humans in power armor very often, because the ones who do end up dead fast. We survive with Agility, taking cover, and force fields, not by virtue of our plating.