It's a personal choice. If you are happy with the Coral Princess, than by all means - pay your cheaper fare and enjoy your cruise.
For me, it's about trust, and show.
I trust Disney (and
DCL) more than I trust the other cruise lines (and to be clear, I have sailed Carnival, DCL, NCL, PCL, And Holland. A long time ago I even sailed Homelines when they existed). I wouldn't step foot on a carnival ship if it were free and as a bonus they were putting my kid thorough college. that's my opinion. Others swear by them. I have had good times and bad times on every cruise line, but I saw this from my personal opinion - DCL of all the lines (and Disney in general) never lets a cruise end poorly. They go out of their way to correct any wrong and have the most sincere (again in my experience) desire to make sure you are happy. They are the only line I know of where the waiter in the main dining gets involved and wants to do something to correct an issue that you had during a show or a character meet and greet. Or your stateroom host wants to help with a problem with the pool.
And it's about Showmanship. Everything on DCL is spick-spec. Always. Everytime. If you get on the ship it's first sailing, 21st or 351'st, it always looks like it's right out of dock. The shows are amazing broadway style. Everything is with a flair that you just don't get on other ships.
I quip all the time (but it's true) we were just as Nassau last week. the lineup with Carnival Fascination, Carnival Fantasy, DCL Dream, Enchantment of the Seas and the NCL Sky. The other ships showed definite wear and tear. Each one needed a paint job. Except the Dream. They were out there hosing her off - like they do every time to keep her clean as a whistle.
Again - these are MY reasons. Each person makes a personal choice. It sounds to me like you have made yours. I won't try to change your mind. I will say that in general, you get what you pay for. That's been my experience as well.