A hard decline for a subscription company means that customer is gone unless you can get them to pay another way or update their credit card. There is no automatic updater or other magic that will make that credit card work again. It's gone.
A soft decline is however just a momentarily interruption. Insufficient funds is the most likely cause. Try again and it might work after they have paid their bill. Or the fraud alert is resolved.
These should be treated differently in the dunning process.
What about credit vs bank vs gift cards: do these differences hold?
Who believes that a subscription service will increase their sales by adding Paypal and digital wallet solution? They certainly add complexity which might make sales worse and certainly make development more expensive.