but individually are to the degree they would score for fun in Serie A too. Like they do in CL.
They will both be on +25 or +30 per season probably. Not sure about Ronaldo, though. When tightly marked, which he will be whenever he plays against a serie A team, he could even end up with less than 20 goals and yes, with even less goals than Di Natale, despite the enormous difference in quality between them.
Lot will depend on the team they're at. Put Messi in this Juventus and Juve will win a lot, but not because Messi will score 30 goals as much as because there will be 3 players around him all the fucking time and the other Juventini will have it much easier. In CL, against the best teams who don't just defend, Messi finds it easier to score with Barca than he would find it if he played in serie A for this Juve, against annoying provincial teams.
We'll have a guaranteed scudetto with him, though.