1. R9 while being an amazingly talented footballer is really not a goat candidate because of the lack of longevity and too little success at club level. He is really difficult to compare to others because whether you like it or not, the idea of "what might have been" definitely comes into play.
2. Cristiano has to be in the list for sure, below the top 3. As much as i hate his personality, his success at club level and longevity means he deserves to be there.
60s: Pele
70s: Cruyff/Backenbauer
80s: Maradona
90s: R9 (based on seasons 1996 to 1998) or Van Basten
2000s: Ronaldinho
2010s: Messi
2020s: ? Yamal
Of these only Pele and Messi can truly claim to have dominated an entire decade.
you can even have Pele for the 50s and Messi for the 2000s because they were that good even in their teens. I don't put Cristiano for 2000s because he was clearly second best just like Platini.
Most decades get split down the middle. It is extremely rare for the dominant force of the first 5yrs to still be the man in the second and many times the lines blur; you might even break it into thirds, which is more appropriate for a few decades.
50's: Puskas, Di Stefano, Pele
60's: Pele, Di Stefano, (3rd is arguable: Eusebio, Charlton, Best)
70's: Cruyff, Beckenbauer, (3rd is an arguable blur between a number of players: Rummenigge, Keegan, Simonsen, Zico, Platini)
80's: Platini, Zico, Maradona (for whatever repute he had, Maradona only went clear and stratospheric in 1986; Platini was in pole position to be the man off the back of a number of incredible seasons in the early 80's before topping it off with arguably the greatest tournament run in the history of the game with his comic book Euro '84), Gullit, Van Basten.
90's: Van Basten, Baggio, Romario before Ronaldo burst onto the scene and made it his own until injury, Zidane.
00's: Zidane, Shevchenko, Henry, Ronaldinho (takes over as the dominant force just as Maradona and Ronaldo did in their decades), then the lines blur again with his decline with Kaka' and Xavi in particular being placeholders whilst C.Ronaldo and Messi emerge.
10's: pointless mentioning anyone but Messi and C.Ronaldo.
Platini wasn't clearly second best as he was delivering at an unprecedented clip in the best league in the world and performing superbly in Europe and internationally; he would've been the Messi of the early '80's in terms of being creator, scorer, game controller and conduit through which entire games were played. He had the most justifiable credentials to have done "a Maradona" at the World Cup,
especially after Euro '84.
As with most things, the spoils of history go to the few despite the reality of their active often being quite a bit more layered and uncertain. Maradona was just as much potential until he proved himself, despite his absurd talent, and that is the story for most and in the meantime there is always someone whose star is pushed to the wayside in lieu of that despite them being huge in their own times as contemporaries. Baggio and Shevchenko are steadily being erased from the timeline, for example despite being a hair's breath from godhood in their own eras.