Ronaldo was A BIG problem but not THE MAIN problem is the best way to sum it all up, no matter what he HAD to go and should never have been signed in the first place.
His ego meant he believed he was above everyone even though it was clear he was done at the top, his stature meant it was going to cause a nuclear problem if dropped which we saw, he disjointed our attack, slowed down our play, stifled others, split the dressing room and publicly went against the manager and his team mates.