AD certainly isn't very big. There's DD (deputy director) between AD and D for most ministries.

But still AD is quite big shot in day to day ops, he/she runs the dept/division/branch etc on a day to day basis.

Much like a Captain isn't a very big shot in the whole scheme of ranks but the OC is pretty much boss in day to day affairs.

Anyway, digressed, it's more useful to compare pay of ranks (MX**) vs titles.