How does that increase the risk compared to something like JBOD or overlayfs? In both cases you will lose data if a drive fails. Keep in mind that this is btrfs raid0, not regular raid. If anything that decreases the chance of corruption because the metadata is redundantly stored on both drives.

No mention of systemd? This is unacceptable.

A disk failure will cause you to lose data, yes. But that’s also the case in all the other solutions discussed here. Backups should be handled separately and are not part of the original question.

Have you considered simply setting btrfs to RAID 0?