It is quite simple, when Ronaldo scores goals, Ronaldo is right, and when he doesn't score goals, Luis Castro is wrong. This is how Ronaldo thinks. Ronaldo can be both a blessing and a curse and as long as he scores goals nobody will complain, but once he has some bad games the trainer has to fear to get sacked. This is why I wonder that someone would think the task had become lighter for him. If it is true, it also became riskier because when bad times come up, it could lead to the end much quicker for a trainer than without Ronaldo.
Usually it is when there are problems that coaches get fired who are also coaches from Ronaldo. The first problem is that Ronaldo doesn't score and then he immediately blames the coach because Ronaldo can't handle his own weaknesses. The second is that the whole team plays bad and then Ronaldo is the first to also blame the coach. The way Ronaldo behaved in the final at the Euro 2016 was disrespectful towards the Portugal coach. Enthusiasm and passion yes, we all love that. But stealing a man the show who actually deserved it is poor behavior. Ronaldo just leveraged his public recognition to the detriment of people who theoretically have been in a higher position than him (coach > player). When he played for Real Madrid, there were barely any discussions because Ronaldo was in his prime. There isn't much to discuss when you win most of the time.