Most distros have a udev rule in place that inhibits a mount attempt of a multiple device Btrfs until all devices are visible to the kernel. The degraded mount option won't even matter in this case, because mount isn't attempted.

If you remove this udev rule and then add degraded mount option to fstab, it's very risky because now even a small delay in drives appearing can result in a degraded mount. And it's even possible to get a split brain situation.

Btrfs needs automatic abbreviated scrub, akin to the mdadm write intent bitmap which significantly reduces the resync operation.