I know what you mean! I have similar feelings about proportions for my EC. If I'm paying forgeworld an obscene amount of money, they better look perfect!
But, if you like the chainaxes that much, you could just get a power armour hand and cut the two parts above and below the terminator hand and just stick them onto the power armour hand? Then you've got the chainaxe but it's also got a sensibly proportioned hand?
The only problem there is that unless you pin it, you're essentially pre-breaking the weakest part of the model, which often frustratingly breaks anyways. Though better that than disproportionately large hands.