Actually we are ranked 5th in fewest errors, and 2nd in missed tackles. If this was our problem, we would be top 4.
I think you'll find it is our output in metres gained, and inability to create line breaks, where we are ranked in the bottom 4. This implies there is too much pressure being placed on our middles, so they get gassed from having to constantly tackle and cart the ball from our own line. If you look at the workloads of our individual players, it's absolutely appalling how little our back 5 actually help