Convenient how you continue to define "unsound" in terms of a 3600+ computer. Also, Judith Polgar became the youngest GM in history playing the KG as one of her main tools. I already said it doesn't do great with GMs.
Define "lower levels". The screen shot below is for players 2000-2500 after move 1. Notice that the third choice, f4 (the king's gambit) wins just 1% less than Nf3 (which can be anything), and a bit worse than the Vienna.
Don't believe me? Go check yourself.
#18
An opening that wins more for black than for white is unsound.
"I would like to play the King's Gambit, but I have yo find a way to equalise for white" - Kramnik
It is OK to play bad openings at lower levels and in fast time controls.