rvp Tried the USB install image and USB boot?
When installing on bare metal, I always use USB install images.
I only use the ISO to create VMs.
rvp You have slices instead of wedges on NetBSD too?
Before hearing about NetBSD, I though wedges were just fried sliced potatoes... 😉
That said, I just use sysinst to partition my disk, so I have whatever it creates for me.
The visible difference between the non-working version of sysinst in NetBSD 9.1 and the working one in 9.99.75+ is a new option surprisingly (and incorrectly) labelled "Delete everything, use different partitions (not GPT)" allowing to successfully and reliably install NetBSD in any context (bare metal, VM, UEFI, legacy BIOS).
[ The option label is incorrect because when selected, it correctly wipes the disk out (which earlier sysinst versions failed to do) and prompts you for the partition scheme to use, including GPT. ]