Looks like we both failed math 
Brazil - 3
Uruguay - 9
Colombia - 15
Chile - 19
Paraguay - 35
Ecuador - 53
Bolivia - 81
The median here is Chile, who are ranked 19th.
The median ranking for Ronaldo’s opponents at Euro 2016 was 26.
Ronaldo only had good games against Hungary (20) and Wales (26). Portugal won against France without him.
Messi was excellent in every game but the final, including fantastic performances against Uruguay (9), Chile (19) and Colombia (15).
Messi’s international trophy is clear tbh.

Brazil - 3
Uruguay - 9
Colombia - 15
Chile - 19
Paraguay - 35
Ecuador - 53
Bolivia - 81
The median here is Chile, who are ranked 19th.
The median ranking for Ronaldo’s opponents at Euro 2016 was 26.
Ronaldo only had good games against Hungary (20) and Wales (26). Portugal won against France without him.
Messi was excellent in every game but the final, including fantastic performances against Uruguay (9), Chile (19) and Colombia (15).
Messi’s international trophy is clear tbh.
There are more stronger teams in Europe than there are in South America, but that's obvious with more countries. I'm not sure of the general point you are making but it seems clear that Portugal didn't meet a lot of the stronger nations, other than Croatia and France, which can happen in a tournament (see England in this Euros).
The way I look at it it's a surprise that Argentina and Brazil don't win the Copa America every tournament, or at least most of them, given their size and player pool in comparison to challenging countries like Uruguay, Colombia or Chile. So for Messi to have won one Copa America is not a huge achievement at his age. Yes it's a team sport, but let's not pretend that he hasn't had his fair share of international flops.
