I will be taking a stroller for our 5 year old on our next trip. It's a clunky 11 year old stroller, but it has great sunshade and storage and is good up to 50lbs, and he's 40 lbs.
My eldest would have not needed a stroller at Disney at 5. He had a trip at 3 and didn't use it much until the end of the trip. At 6, he went and we were not easy on him with the walking, and he did great. My middle child wasn't supposed to use the stroller when she went at 5, but the youngest refused to sit in it so it made sense so we weren't always pushing an empty stroller. I would have not brought one for her. Then there's my youngest. At 2.5, he refused to use the stroller so we had to use the sling, since he also refused to walk. At 3.5, I figured out how to bribe him to sit in the stroller at times - since again, he wouldn't walk. At 4.5, he actually enjoyed the stroller. He refused to do many rides and was a bit overwhelmed and the stroller allowed him a place away from everything. He does have some sensory quirks, so it helped out then, and I presume it will help out again on our trip this year. So, consider both the walking and if the crowds/attractions will overwhelm the child. My youngest is perfectly capable physically, but he really needs a spot to call his own to hang out for emotional reasons.