Ask a Thief Thread.

Most people make it sound like they are crap, but those seem like useful skills to have. Like, immobilizing monsters when you're out of stars and throwing money at them, then running like hell. Or using Shadow Web to hold monsters down so you can use Avenger on all of them.

Maxed Shadow meso was actually more powerful than lucky 7 back before all attack boosts and 4th job. Now it's just pure trash. Also with shadow stars, if you run out of shurikens, you simply aint carrying enough.
Shadow web is not too useful because the bind effect is canceled if you attack the webbed monster. The only real use would be on event monsters with a crap ton of HP and no boss flag. It can also be used if you are sniping at a semi dangerous spot and need to make monsters behind you stand still. That will never happen after 4th job though.