PSG forked out a world-record fee of €222 million (£198m/$263m) to bring Neymar to Parc des Princes from Camp Nou in August 2017.
The Brazilian had established himself among the very best players of the modern era during his time at Barca, scoring 105 goals in 186 matches while also getting his hands on two La Liga titles and the Champions League.
However, he struggled to reach the same heights during his first two seasons at PSG, with persistent injuries and disciplinary issues preventing him from fulfilling his full potential.
Neymar pushed for a return to Barca last summer after growing frustrated with his situation in the French capital, but the Spanish giants were ultimately unable to reach a final agreement with his current employers.
The 28-year-old bounced back from that disappointment by getting back to basics behind the scenes in Paris with a view to rediscovering his best form.
Neymar ended up inspiring Thomas Tuchel's men to a domestic treble as well as their first-ever Champions League final, but could not prevent them from losing 1-0 to Bayern Munich in the showpiece event earlier this year.
The ex-Barca superstar has since insisted that he is happy at PSG, and although his injury problems have returned at the start of the 2020-21 campaign, Rafinha thinks a fellow countryman is now in a far stronger place mentally than he ever was at Camp Nou.
The 27-year-old midfielder, who played alongside Neymar in Catalonia between 2013 and 2017, told Telefoot: "I found a much more mature player than at Barca.
"Neymar is world-class, one of the best in the world. It's a privilege to play with him."
Rafinha was speaking ahead of PSG's crucial Champions League clash with RB Leipzig on Tuesday, which they cannot afford to lose after dropping to third in Group H following a narrow defeat in Germany on matchday three.
"The game against Leipzig is extremely important. It is a key meeting, and there is only one way out of this meeting: it is by winning," he added.