The fact that Airbus are fly by wire doesn't mean they are "unstable".

They might be, but fly by wire does not imply that.

For the record, I don't believe Airbus plans are unstable in the way the MAX is, whose instability, from what I understand, came about because they were trying to fit larger engines on the original 737 frame (to prevent pilot retraining), and so had to move the wings higher.