Over a 50 year period I've visited Reims and Epernay many times and visited many of the "big" champagne producers, at the end of the tour you get to sample (for a fee) some nice champagne--I'm certain none of these had apple under/over tones.
Yes, what I was served in flight was (as noted in #8 ) Gardet.
What is most annoying (to me) is that AA in their Flagship lounge and DL in the SC serves some nice champagne, yet on the plane they serve stuff of lesser quality.
I think you are 100% justified in your complaint. The quality of DL catering has been deteriorating at a rapid pace. My first overseas J flight on DL, which was only a couple years ago, the retail price of wines was $25-$30. Now it is down to $10-$12. Domestic F is even worse for wine. Food is also going downhill quickly. I think I do have realistic expectations...perhaps a $20-$25 retail wine in intl J and $10 retail wine in domestic F. Most of my flights are on my own dime...and although I do not specifically book the flights I do for food or wine, it is part of the overall experience, and when a part of the experience becomes cheap...then the whole experience becomes perceived as cheap. Therefore, I do not buy F/J unless it is REALLY cheap...like the experience I receive.