The main aim of signing Ronaldo for Juventus was clearly to win the Champions league, which they didn’t achieve. I see this as the main reason why people claim Ronaldo wasn’t a good signing for Juventus. As well as him being one of the main reasons for Juventus’ economic issues.
He played very well, but it was a bad decision, and wasn’t the way the go for Juve if they really wanted to remain on top. The team was aging and bringing in Ronaldo wasn’t going to stop the team from aging and gradually regressing without any other signings. An unfortunate transfer for both sides, Juve crushed their financials leaving them no room to buy top players (Particularly in the midfield), and Ronaldo spent 3 years of his career with an aging team that was getting worse and worse despite him scoring as much as he could.