Perhaps it will be so, perhaps Ronaldo will end his career in Juventus, after all, age plays a big role in football. And I doubt Ronaldo will go to play in China or America in pursuit of money. Juventus is a good club, and with Alegre the results can be very good, I don't know if they can compete with dignity in the Champions League, but they can become champions of Italy.
Italian clubs rarely ever do good in champions league anyway, at certain point they were not so bad but in over 10 years they haven't won the UCL so far, which was also the period where Juventus became champions back to back so many times. Before that Inter had one and milan had few, but that was looong time ago. So I think same will go on, we are going to see in fighting at Serie A for sure but no Italian team will be doing any good in the UCL that is just not going to happen.
However with the additions of new names, and changing stuff in Serie A we could maybe see some more competition between teams, I do not think that it will be a clear winner, when you look at teams now, even with Ronaldo staying at Juventus, can you say who will be champions? I think there are 3 even maybe 4 teams (realistically 3) that may end up being champions.
But still, when Ronaldo moved to the Italian championship and Juventus signed a contract with him, it was clearly implied that both sides wanted to win the Champions League, and winning the Scudetto in Italy was taken for granted. Although, of course, increased competition in the fight for the title, in principle, should increase the overall level of clubs, and therefore increase the chances of winning international titles. Juventus has not won the Champions League for a long time and with the arrival of Ronaldo, with his experience of winning, he hoped for a quick achievement of the cherished goal. But the goal has not yet been achieved and the team was left even without the title of champion of Italy and hardly got into the number of participants of the Champions League, so it will be interesting to see the results of Juventus in the new season with or without Ronaldo.