That won't work because sshd runs the command using the user's login shell. From https://man.openbsd.org/sshd#LOGIN_PROCESS:

> When a user successfully logs in, sshd does the following:

> ...

> 9. Runs user's shell or command. All commands are run under the user's login shell as specified in the system password database.

Logging into another shell would be attempted only if someone knew at the time why the logins were failing.

But thanks, I've just added another technique to my toolbox.

Depending on the distribution, /bin/sh might be a symlink to bash

On a Linux box isn’t that just a link to bash?