It depends on what you are looking for? Are you simply looking for a cruise or are you looking for a cruise that's immersed in Disney? If you don't care about the immersed-in-Disney part, you may be better off price shopping other cruise lines.
I respectfully don't think it is that simple. There are so many other factors that differ between DCL and other lines, with Disney-immersion only being one of them. While we like some Disney immersion, we like to keep it light, which DCL mostly does compared to some of their hotels like the Art of Animation resort. Disney theming is also only a "nice to have" for us and isn't high on our priority list anymore, yet we keep coming back to DCL.
Beyond the Disney immersion, I would say these are many other considerations between lines. Just a few that come to mind are the style of the ships (classic ocean liner vs. Vegas hotel or local mall feel); service level, including turn down service, cleanliness, room size and layout, indoor smoking rules, itineraries (DCL's biggest weak point); dining experience, including variety of dining options and flexibility; the type of activities offered on the ship (including paid ones); adult pool/sundeck experiences; adult nightlife, in both style and hours; type of customers and what they are also seeking in the cruise experiences, what is included, and other simple things like towel management policies, ease of booking, checking in, excursions, online communities that add to the planning and fun (DCL has the best!) etc.
The truth is we have limited experience with other lines, but keep coming back to DCL because it just works for us and the potential downside of a bad experience on another line is rather steep, since you only get a certain amount of vacation opportunities. It doesn't mean we are opposed to trying other lines, which we are doing soon, but it means we do so very cautiously. But we know DCL is a great fit for us and don't mind paying a reasonable premium, even without young kids and even though we don't need the Disney theming to be happy.
All that said, the question can't really be answered. The premium varies significantly based on the itinerary, when you book, and time of year you are sailing. I have found some itineraries that there really isn't a premium at certain times of year, for similar rooms, after all costs are considered. Everyone's financial situation is different too, meaning the premium is more of a consideration for some vs. others, and everyone's tastes and vacation desires vary too much. The key is to watch a bunch of cruising vlogs and get a good feel for whether it is worth it for you. In today's world, you can get a very good feel of what the experience on different lines will be like. I guess I would say, I would probably stretch my budget to try it with young kids if you can, but probably not stretching it too much for adults who are happy on other lines, even though it is worth it to us.