you're right, but this can be solved on the client side e.g. with:
Code:
proxmox-backup-client snapshot list ct/ID --output-format json | jq 'sort_by(."backup-time")'
you can ofc open a bug report (https://bugzilla.proxmox.com) , but i guess this is simply done to be faster (since we read the snapshots in order we get it from the disk) and sorting would slow down the api request