Are the "stable" operations comment just diplomatic words or fact ?
Is it terribly important one way or the other?
Once in a while they publish dispatch reliability statistics - you can look at the numbers and draw your own conclusions.
Also ANA is not the only operator of the 787, is United for example writing angry letters to Boeing complaining about 787 unacceptable dispatch performance? They once did, in 1996, it then made headlines, United was bitterly complaining about 777's poor performance, still too many problems in the 2-nd year after its introduction to United's fleet, clearly United was unabashed and did not hide behind diplomatic words. Now the same 777 is the epitome of reliability among jetliners.