ronaldo is not your classic CF. when he's not standing in the box to feed off crosses or mistakes, he makes runs from deep/outside the area.
doesn't combine that well or works for others by occupying and battling opposition defenders.
neymar and messi already have kind of free roles and come running with ball on feet from deep. why would you want ronaldo to just stand in the box?
suarez in his prime years with MSN was perfect because he enjoyed doing the dirty work and opening up space for messi and neymar.
He doesn't need to do a whole lot if he has Messi and Mbappe setting him up. Also, I feel Ronaldo would rather move to PSG than join City.