@FunkyMonkey i did a quick trial and it seems you are correct. An interesting bonus for using multiple smaller commands.
Alternatively you can use post processing on the repo to extract the information. For example restic ls -l snapshot_id lists the entire snapshot file tree including sizes. There is a tool redu on github that does this, like ncdu. I have not used it myself but it seems to provide what you are looking for.
EDIT
Also restic itself can do it apparently, see the docs about the ls ncdu option. Working with repositories — restic 0.18.1 documentation
restic ls latest --ncdu | ncdu -f -
or another example
restic ls --long latest --sort size --reverse