>For these reasons, 1.6mm sure seems like a default if there is one.

If you do consumer (phone/tablet/pc) a lot of boards are 0.8mm(12L) or 0.6mm for example.

If you do automotive/drones/industrial it’ll become thicker (2 oz copper).

DirtyPCB defaults to 1.2mm. I measured a couple random dev/breakout boards around and got 0.8/1.2/1.6.