As someone who is currently playing a blade song, they are definitely okay if not a bit too strong. The only weird thing about them is that extra attack messes with how you probably wanna play the class, so I’m fine changing that.
If I added your defense to my blade singer, his AC would go from an already absurd 25 to 31, 36 with shield. That’s definitely crazy. The last thing bladesingers needs is more armor.
If I were you, I would just change out extra attack. It’s the one thing that doesn’t quite make sense. Maybe move song of defense (which is fine at 5 per spell level. I would make it 2d6 per spell level at max) to level 6, and add an attack buff at level 10.