I will start by acknowledging that a weaker Brazil changes a lot as far as attention and excitement. When they are the world's best it adds something, but still a gap.
But the quality, game flow, passion from fans, stadiums and attendance, refereeing, I honestly feel like I am watching the SEC vs everyone else. I used to scoff at those saying it's harder to win the Euros than a WC but watching this year and the games played in the round of 16 at the Euros vs what will be played in the quarterfinals of the Copa, it's not even close.
Copa America almost has no choice than to make this a combined event with CONCACAF going forward just for relevancy... having the 10 teams play each other won't capture the world interest until you get to the final 4.