4 small drives+raid gives you redundancy.

And often are about the same price or less expensive than the one 8TB NVMe.

I'm hopeful 4/8 TB NVMe drives will come down in price someday but they've been remarkably steady for a few years.

Given the write patterns of RAID and the wear issues of flash, it's not obvious at all that 4xNVME actually gives you meaningful redundancy.