Ultimate Chaos Sword not big enough for marauder to wield properly

The ultimate chaos sword two-handed weapon MTX does not fit like a two handed weapon when used on a marauder.

link to imgur: http://imgur.com/a/nkOg2

You're not using it on a sword - it has nothing to do with the weapon's size. You'll note that he's holding the weapon the same way as he'd be holding the base weapon you've put the cosmetic on.
Even if they made it big enough that, you know, your characters left hand would actually be on the weapon, it would still not look proper.

But since you CAN use it on other two-handed weapons, shouldnt it be made to fit that too? It seems kind of,...well,...important?

Oh, certainly. My opinion is that as long as this issue exists, they simply should not allow you to use weapon skins on weapon types they weren't meant to be used on. Currently, it just leads to disappointment and people feeling they were screwed over, seeing that they could use a particular skin on their current weapon and buying it, only for it to look at best silly or at worst terrible.
This should not happen and whether they resolve it by restricting what weapons these skins can be used on, or making it use the animations associated with the weapon type of the skin rather then the base weapon that's actually being wielded doesn't matter to me, personally, as long as it does get resolved in some way.

My point was simply that scaling up the sword might improve the situation a little, but doesn't solve the issue and still would not look proper. I'm all for actually solving the issue, because buying a skin that you're told can be used on your current weapon only to find using it on your weapon isn't really properly supported - that just leads to refund requests and unsatisfied customers.