Ronaldo woudnt get in our team because we depend on tenacity , workrate and energy from all ten outfield players , one player not contributing is a 10% drop and that is enough to lose games. Ronaldo is in a team that has to rely on flashes of indivduality because the team he plays for does not have a work ethic or any tatical structure.
As for Ronaldo being responsible for Juventus's demise in Serie A ,maybe an ageing team with the likes of Chiellini , Bonucci , Rabiot and losing Donaruma a world class keeper has some influence on their current situation, and the disastrous decision to bring back Allegri after two years twiddling his thumbs in the football wilderness ,although no doubt losing Ronaldo is a part of the reason for their struggles.
Would Juventus still be challenging for Serie A if Ronaldo for was still playing for their team ? , absolutely not there are many other contributing factors , the reason Ronaldo left Turin was because he could see it was going tits up and nothing he could do would change it.