My lad still has 3×9 – specifically, he has my old 3×9, as I’ve gone 1×11. His sister is 1×10 and his mum is 1×9.
Are you missing out? Not if you are happy with it.
fwiw, I don’t “miss” 3×9. I run a 32T up front and 11-42 at the rear. Most of my local riding is flat, smooth, non-technical bridleway bashing, and I spin out at around 20mph, while having plenty of low gears left on the local hills. I’m thinking of going 34T up front and taking my chances on any big draggy climbs if I’m riding away from home.