The British withdrawal to Sicily most certainly does make it a strategic defeat.

That certainly wasn't the British Army's view of things. To them, the only strategic goal was possession of Sicily. Period. Read "Counterpoint to Trafalgar."

So, you are simply wrong in regards to the British strategic interest's being damaged.

However, from the Court of Palermo's standpoint, the withdrawal was a strategic defeat, because their only interest was in regaining Naples.

From a French perspective, at least in N's view anyways, gaining Calabria was only important as a jumping off point for a descent on Sicily; because his only strategic interest was Sicily. Read N's letters to Joseph.