The default should be the device's native blocksize, and some devices misreport. You also lose performance if you use a larger blocksize than necessary.

If we can, I'd like to get a quirks list in place, but there have been higher priorities.

Do each of the other filesystems have their own quirks list? That seems suboptimal. Oh, I guess it's because it's in the user space mkfs tool of each, not the kernel.