Perhaps we have different opinion, but I think local competition such as EPL, Serie-A, or Champions League has bigger number of fans because it is not limited to where we do live.
For example a team like Real Madrid, their fans base are all over the world from many different countries but if we talk about National Team then it is limited to their own country.
In case of potential betting, I have no valid statistic about how much is the average betting amount placed during World Cup compared to Local Competition/Leagues.
But for sure every competition has its own market and perhaps World Cup has a big market because this event is not happening every year.
Yes, we have our own views on this. Because I myself do not have valid data regarding the number of fans from each country. Indeed, logically the club will be wider than the national team, but for teh national team and nationalism from people of each participant will add to the euphoria and team spirit. As for countries that have won the title, such, Brazil, Germany and so on, they will get support from fans from countries that did not participate.