Be very careful when reading opinions on which line has better food. We haven't been on a ton of cruises, but have sampled a few and food quality can vary from line to line, ship to ship or even night to night. I've been on the Wonder most often and I remember getting off one cruise thinking I liked RCL food better then the next time on the Wonder I felt like the food was way better. Our last cruise we had great food three nights and then night four I thought we had changed ships or something. There are so many variables when serving that many guests, not the least of which is guest personal preference. The one thing you get with Disney that I have never experienced on other lines I've sailed is that they really care about food quality. When we have had an issue, we had the chef come to our table the next night to personally apologize.
My wife and I have sailed Disney as adults and also sailed with our adult children. We like DCL because we love Disney and we love the service and vacation experience that Disney offers. What I'm sure you noticed on the Dream, Disney is everywhere you look and everything you hear. While the Disney universe has expanded with Marvel and Star Wars, it's still all Disney all the time. If your party isn't all in on the Disney bandwagon, they may not enjoy a
Disney cruise as much as you would.
If you love broadway musicals and big productions, then DCL offers the best option there. My wife and I are picky about show quality (lots of reasons) and there is no comparison really. Disney brings the best talent on board their ships. Carnival knows how to create a production show, but they struggle to execute. Yes, the people on stage are more talented than I am, but that's not saying much. We have also enjoyed the RCL shows, but they just are not as good as Disney, even though we noticed RCL (at least at the time we last sailed) had live orchestra with the production show and DCL does not.
DCL accommodations are very good. I can't speak to how each line compares in terms of accessible rooms since you mentioned one member of the party uses a
scooter. You'll want to research that carefully. I've seen scooters on all ships so I don't think that would be a problem wherever you go, but some ships may be better than others for scooters.
Not sure why you have ruled out ships smaller than the Dream. We've sailed the Wonder a few times and would definitely recommend it. Smaller ship does not necessarily mean smaller spaces. It means fewer people for sure. While the Walt Disney Theater is smaller, the relative scale and fewer passengers make it just as grand.
If you really want to learn what other lines are like, there is another message board that caters to cruising in general that I recommend you check out. It's called Cruise Critic.