Author here. I don't claim sshpass is "broken by design". I claim it is brittle as it relies on the detection of a password prompt. passh author has several examples here: https://github.com/clarkwang/passh/blob/master/sshpass-broke....
On the sidebar, in the about, it says,
> sshpass is broken by design
This is another repo. But probably where they got it.