I disagree. Start to finish, Back in Black is easily their best album. That said, I 100% believe that album was written by Bon Scott as it was released 5 months after he died. They stripped Bon's family of their owed monies. (AC/DC are not good people)
After Back in Black, they had very few good songs, but there were a few. I can think of three of the top of my head For those about to Rock, Who mad Who, and Thunderstruck. Their could possibly be more, but they aren't coming to me.
If you subtract the Back in Black album, I pretty much 100% agree with you though.