On my rhel7 system, the Debian dash shell is this large:

   $ ll /bin/dash
  -rwxr-xr-x. 1 root root 113536 Nov  5  2018 /bin/dash

I happen to have an old powershell installed:

  $ rpm -qi powershell | grep Size
  Size        : 126588370

A strict POSIX shell is always going to be vastly smaller, for many reasons.

I would prefer that the POSIX shell was an LR-parsed language, but you can't have everything.