Tough topic, Rivera is hugely revered in Italy but outside not as much probably due to the lack of a stand out WC. Looking at the Ballon d'r rankings it shows he was amongst Europe's best for a decade.
Firstly we have to establish zico primarily functioned as a playmaker or was he in fact a deep lying forward/inside forward (ie a goal scorer with outstanding playmaking abilities) Rivera was more of a conductor ala Xavi but could dribble like Andres iniesta and score better than both (and he also did it in a more defensive era) Zico as a finisher can rival the best in the history of football 500+ goals in his career the majority scored in state championships but if there was any doubt he settled that in 83/84 when he outperformed/outscored ballon D’Or winner platini in Serie A (Zico had a higher gpg on a lower scoring team that had a much worse defence) They are totally different types of playmakers to begin with Rivera played deeper and zico was more offensive Zico was definitely more complete but did not (as far as I know )dictate matches on a regular basis He was more an expert of the final ball than ball distribution if that makes sense I could be wrong but that’s my take
I am pretty sure Zico could have played the conductor type of role. He had all the right attributes to do so. Long pass, short pass, could be evasive with the ball, good decision making. Perhaps defensive work would be the only skill he'd have to prove. But since he was great at scoring goals, he played more like as you said closer to the goal.
Rivera himself wasn’t known for his defensive work rate (at all) so he proved that defence ability isn’t a prerequisite of being a deep lying playmaker (it helps when you have a DM like Trapattoni covering your back- I’m unaware of any Brazilian player like him) I also think Rivera’s decision making was of an elite GOAT standard (rarely do you see him misplace places and his array of passing was in my IMO also better than zico) Zico was better in shooting ,final ball assists,FK,header,,dribbling But if we’re talking about playing just as a midfield boss Rivera is much better(that was his position for His whole career and we can only speculate on how zico would’ve fared playing predominantly in this role)