Not true. The first 2 seasons Juve were considered one of the strongest teams in the world. This season the team has performed very poorly.
Here are the stats (FACTS) no "feeling" here, these are just hard numbers/facts:
Comparing 3 year prior to CR vs 3 Year after CR (Just comparing Serie A/ Coppa Italia and Champions League)
2015-16: Champions - Serie A with 91 points | Champions Coppa Italia | Round of 16 eliminated by Bayern in Champions League
2016-17: Champions - Serie A with 91 points (again) | Champions Coppa Italia | Runner up (Real Madrid Champions) of Champions League
2017-18: Champions - Serie A with 95 points | Champions Coppa Italia | Quarter Finals in Champions League - Eliminated by Real Madrid
----- CR JOINS----
2018-19: Champions - Serie A with 90 points | Quarter Finals Coppa Italia (Eliminated by Atalanta) | Quarter Finals in Champions League - Eliminated by Ajax
2019-20: Champions - Serie A with 83 points | Runner up Coppa Italia (Napoli winners) | Round of 16 in Champions League - Eliminated by Lyon
2020-21: 3rd right now (27 games played) 10 points behind leaders Inter | In the Final of Coppa Italia | Round of 16 in Champions League - Eliminated by Porto
Summary:
3 Years prior to Ronaldo joining Juventus won: 3 Serie A title / 3 Coppa Italia / Made the final of Champions League
3 Years AFTER Ronaldo joining Juventus won: 2 Serie A (they are 10 points behind Inter for the current season) / 0 Coppa Italia (they are in the final for this year, so at best 1) / Highest place in Champions League? Quarter Finals.
The above is just FACT, no feeling no biased, nothing, simply facts.
Now how Juve were considered of the strongest teams in the world while doing WORSE than prior 3 years, is something I am not sure I fully understand.