I say it's worse to direct a bad script than to write one.

If you're directing a bad script, you can rewrite it, either yourself or bringing other writers in. You can shoot stuff, see what works and what doesn't, and change it. Hell you can scrap whole scenes and have the actors improvise the dialogue.

If you're just writing the script, you have to just imagine how it's all going to look and sound on screen.

I think it's a cop out (pun intended) if he thinks he can just say hey it wasn't my script and let it ride on that. If anything the writer can say they fucked up his script, and it's a far more credible statement.