Ronaldo's position at Juventus was only as a complement, when Ronaldo came, Juventus was at the peak of its glory. Ronaldo came to Juventus at the right time, even without Ronaldo Juventus had won the Italian League in a row. Now just look at Manchester United's performance, if Juventus' success is considered the Ronaldo effect, why at Manchester United Ronaldo cannot improve Manchester United's performance.
Cristiano Ronaldo is one of the best and toughest player in EPL Currently, but let's assume that United aren't in their best form this season. Ronaldo came at the wrong time for United and it isn't a good news for Ronaldo. Perhaps with the United board bringing in the New manager, Erik Ten Hag who will make tactical changes in the team and Ronaldo is in his plan of changing united squad. It's very a promising situation for Erik to lift trophies with United team. The new boss will make some few signings for the team.