Deleting both doesn't mean not having the number of the physical saved somewhere secure. It just prevents a card from being drained of your Disney account is hacked. If I were to lose the physical, I would address that by quickly adding it back to the Disney account (from the saved location, I use a password manager) then transferring the balance to another card in my possession.
Though I like doing, even better, what you already do: just charge to the folio as much as you can and pay it off the night beforeb with a gift card.
As to whether the CC is worth it without using the $200 credit, I think it might be if you max out the other two credits. Still a net savings if you don't already get D+ free with some other CC and can use $100 off tickets. Of course it's a lot better if you can max the $200--doesn't have to be in one stay!