I just priced out 7-day Eastern Caribbean cruises within a 2 week period in October (my only open window this year), using similar criteria as best as possible across all:
DCL: $3,200
RCL: $2,200 (~70% of DCL)
Celebrity: $2,100 (~66% of DCL)
NCL: $3,300 (~103% of DCL)
I don't consider a price differential of $1,100 for 7 days as much of a price difference despite the 35% spread. I don't think that this means that I'm kidding myself, full of it or blinded by Disney rose-coloured glasses - I suggest that perhaps our metrics regarding what constitutes "much of a price difference" are simply different. Those are the numbers as best as I can determine based what I consider to be the best apples-to-apples comparison I can come up with. This is my experience. YMMV depending on a significant number of factors.