I have to disagree with you:
The "best for families" maybe... but in other Categories, they rarely make it to Top 5 (Crystal, Seabourn, Viking & Azamara usually take all the spots).
One of my friends was a TA (he unfortunately passed last year) and he told me that
DCL cruises departing from San Juan, Galveston and NYC were not selling out and they were pretty much filling up the ships with TA's (I'm not giving out the price but he had 7 nights cruises in a verandah cabin for less than what I paid for a 3 nights in an inside cabin)...
Hmmm. Interesting choices. IMHO you are comparing Apples to Oranges as every line you listed is actually NOT a competitor to DCL. They are small to mid sized ships, not Oceanliners. That's a horse of a different color. In fact, when DCL announced 2 new ships, the industry was debating if they intended to create river cruises and ships of small-mid category to compete with the very companies and industry you list.
However, for entertainment value:
Crystal - hardly cheaper than Disney. Kinda makes my point. Sure, there is more than one nice steakhouse in a city. The point remains that you pay more for a nice place than an applebees. Crystal's cruises are in many cases more expensive then DCL. They also have very small ships and are not really a serious competitor in the ocean liner category where DCL plays.
Seabourn - Also not generally my cup of tea. In fact, I really don't see them ever rated in the travel sites. I think they are generally more pacific ocean?
Viking - Viking is very nice and often gets good ratings, but they are not ocean liners. They compete in the range of small ships largely doing river cruises.
Azmara - They are the little sister to RCL, right? They do not compete with oceanliners as they are small ships with limited activities (RCL and Celebrity own the ocean liners).
For 2018, Disney scored Best for Families and Best in the Caribbean from US News.
They have scored #1 cruise lines several years from Business Insider.
Escape gives them 4.3 / 5 stars (the best rating for any cruise line)
In fact, they often hold the #1 or are in the top 5 for a number of categories including: Best Cruise line for Families (as you note), Best cruise line in the Caribbean (based on ratings, itineraries, activities, number of ports of call), Best Cruise Line for Entertainment and best for Cleanliness.
Regarding what your friend told you, I do not know about ships leaving from other ports of call. I just know that the ones out of Canaveral and Miami are usually very full. The others that I have been interested in out of other ports of call are often at a premium for space.
However, I also believe what my eyes tell me over that I may have heard from a friend or what someone else on a forum believes. Disney wouldn't make a profit sailing out of Galveston filling the ships with TA's. They would either move to another port, reduce their price or make other changes. Given that none of those things have happened and they have sailed out of that port for years, logic to me dictates that the ships are filling enough for it to be worthwhile. Or are you going to try to convince me that Disney enjoys losing money? Because as a stockholder, that bucket doesn't hold water. DCL continues to outperform the other divisions in Parks and Resorts including the international markets. Given that this is true, and it cannot be supported purely from the Fantasy and Dream in the Caribbean, logic dictates that these other ports of call are making their own turn of profit which again leads me to conclude that they will not likely be lowering the price in those ports.
