It depends on the dataset. If the dataset itself is very large, just walking it to figure out what the incremental part is can take a while on spinning disks. Concrete example - Immich instance with 600GB of data, hundreds of thousands of files, sitting on a 5-disk RAIDz2 of 7200RPM disks. Just walking the directory structure and getting the ctimes takes over an hour. Suboptimal hardware, suboptimal workload. The only way I could think of speeding it up is using ZFS itself to do the backups with send/recv, thus avoiding the file operations altogether. But if I do that, I must use ZFS on the backup machine too.
I’ve yet to meet any service that can’t recover smoothly from a kill -9 equivalent, any that did sure wouldn’t be in my list of stuff I run anymore.