I’m probably missing something obvious (glad you are there 
)
I take as example the command used there for simplicity
midclt call pool.query '[[ "name", "in", ["*"] ]]' | jq -r '.[].size'
This give me the same result as zpool list as you already pointed, but for the stripe and mirrored pool, this seems ok… For the raidz2 pool both are ~6tib and not what I would expect (~4tib)