You will get lots of opinions I guess!
Firstly I'm not sure that EK downgrades often - you are more likely to hear about it though than about a flight that goes to plan (for what it is worth I have flown around 25 sectors with EK in F and never had it happen to me or my wife).

Pluses for me include:
More personal space and a larger bed.
Use of the F lounge in DXB (I think this is much better than the J lounge - space, quiet and food)
Generally good service on board and dine on demand.
Some rare and interesting wines on occasion.
The shower is a novelty.

I'm also happy enough in J and you have identified that it ticks all of the important boxes for you. Quite a nice choice to have to make