Deckware is just a tool to transform that raw entropy into a hex string. But it's not really adding to it or removing any enotropy from it.
But you only know that if you can audit the code, and the reason many people opt for a physical means of generating entropy is because they cannot audit the code of their wallet to confirm how it is creating entropy in the first place. If you cannot audit the code, how do you know there isn't some fatal flaw or maliciousness which means it is spitting out one of a very few number of possible results, or it is introducing a heavy bias?
There is a fix for that though, if you take a magic marker and mark a big X along the width of the card deck.
I've not tried this obviously, but I would imagine any two adjacent cards would be incredibly similar and therefore difficult to be 100% sure of your order. Compound two swapped cards a dozen or so times, and your coins become almost impossible to access.
What do you think about a little bingo machine that has a bunch of balls in it numbered like 1 to 80 or something?
But why? What do you think you are achieving with this over much simpler and provably secure methods like /dev/urandom or unbiased coin flips?