I'm assuming you meant "that's not how Nagato starts fights off"
Ad why the hell not ? Nagato was the leader of the organization Itachi was a part of. He knew all about his techniques, and his talent in Genjutsu, do you think that he wouldn't watch out for those techniques ?
If Nagato had no knowledge at all on Itachi, then Itachi might be able to defeat the six paths of Pain, but the fact is that you still haven't come up with a way for Itachi countering Chibaku. I repeat, stating that "a character>>>>>>>>>>>>>>>>>someone easily" and explaining it by saying "he could just grab him and put him in a Genjutsu" is not the way to do things.