Rivera has basically had various degrees of mediocre talent since he has been here, and he has had a modicum of success. It's also arguable that he has done a pretty fair job making the transition from a DC to an HC. The only real finger pointing I do at Rivera is his decision to keep Shula at the expense of Hue Jackson.
As for the way that this season has gone, at the end of the day we are 3-3-1 with the division lead (ugly as it has been). With the dearth of talent, which is squarely on G-man's shoulders, if he's going to pull the plug on Rivera because of this crap, then he needs to pull the plug on himself.
If you are suggesting that maybe Rivera had a lucky season last year, then I could easily say the same thing about G-man. This offseason, including the draft, up until now has not looked pretty. It just bespeaks of gambling with the risk of possibly tanking because of deficiencies on both sides of the ball that were outright neglected.
It could be argued the team in general had a 'lucky season' last year. Nobody expected us to be that good.
Honestly, given all the injuries, you could argue we're having an 'unlucky season' this year