I've not used BTRFS,  but I do use ZFS on both my desktop and server machines.   I haven't experienced the hangups you do coming out of standby.
But what I did want to point out is that ZFS offers incremental backups using the zfs send and zfs receive commands.   I use these to snapshot the zvol (zfs volume) of a running virtual machine and incrementally back this up to my backup server,  as well as incrementally backing up zfs datasets.