I don't think it's crazy at all that people compare them and consider them close.

Let's say you have what I think of as your average maybe commenter here or football fan. Most of the matched this person watches are in a league other than La Liga, and most of the international games (particularly tournaments) are European rather than South American. This person mostly sees Messi and CR7 actually play from highlights and the occasional CL match or (in Cristiano's case) a match for Portugal.

This person doesn't think a whole lot about "the best" debate but considers it and fills in the gaps looking at Messi's and CR7's total number of goals scored and the "prestige" of the trophies won. I think they could easily think it was pretty close, or the CR7 was better, or that it was just a matter of taste.