Hi, Holly!
Congratulations on your "surf and turf" vacation aboard a Disney Cruise Line ship and to Walt Disney World!
As far as being "better off," it really depends on what you mean and how old your children are. On a Disney cruise, you really only need a stroller if you have a child/baby that doesn't walk at all or is difficult to manage without one. Although the ships are big, it's easier sometimes to move about the ship without a stroller. There are strollers for rent on board -- but there are only a limited number. The most beneficial reason to have a stroller is at the ports of call and especially at Castaway Cay.
Strollers come in really handy at the parks where more walking is required. For my kids, we needed the aid of a stroller until each child aged past five. You can rent one at each of the parks and at Downtown Disney, but it is far more efficient to have your own. My kids seemed to always fall asleep in their strollers as we were exiting a park -- which makes it difficult after you've returned a rented one.
So, in short, strollers are helpful but not essential on board a Disney ship, but crucial at the parks. To save a little money, I would bring one for the entire trip. You will have it in case you needed it for the cruise, and you can store it under the bed if you don't. You will appreciate having your own at the parks. I hope this helps you plan.
Have a wonderful day and a magical vacation. Bon voyage!
Andi