We just bought world class, world cup winner, champions league Varane, and our defence is no better than before. You'd think that would give people a hint as to the actual problem.
Regarding Ronaldo, I suspect his main discontent is Ole's abysmal man managing of him. At this stage of his career back at one of his boyhood clubs which has been struggling, I'm sure that he wouldn't expect to win the league or CL immediately. He'd want to, but he wouldn't be pissed if it didn't happen.
What would piss Ronaldo off is anything denying him his chance at competing for the golden boot in the PL. Even at Juve where he under-performed relative to expectations (aka didn't win the CL), he was still top scorer in the league, and that was still important to him.
Things like being needlessly rotated for games, or being denied penalty and freekick duties that he's enjoyed his entire career, will no doubt come as a shock and demotivator. He's got to be asking himself, if I'm obviously not going to win anything here, and the manager seems hell bent on preventing me from being the main man or in the running for the golden boot, then what the hell am I doing here?