I agree. I'm sure he's not a poor defence coach. His record prior to his ban suggests that he's very good, but as you say, his system didn't work with us.
You'd think that a very good defence coach would have multiple systems and can adapt to different skills and scenarios - the same as we would expect an attack coach to be able to adapt their styles to suit the players.
There's lots of talk on DW that we should just go out and get a great defence coach.NOW.
I think that this appointment after interviewing a number of people suggests that there just aren't many good coaches available at this time.
As an aside, in football, a new manager often brings their own team in who have all worked together previously. It means that the entire coaching team know each other, know they can work together and know their systems work together.
It rarely happens in rugby and maybe it's something that would be a benefit.... Albeit that it takes time to develop that kind of team.