Baseball is virtually unknown, and has zero spectators in most of Asia and Africa. In South America where baseball is very popular it is still less than football.
I lived in Asia for 20 years and cities with 10 million people like Bangkok, Jakarta, Shanghai would come to an absolute standstill for key international matches on TV. The last world cup had a total of 29 billion spectator views.
Only someone that hasn't lived extensively outside of the US would every attempt such an assertion. Besides that baseball is a) not the most popular sport even in the US b) has declining viewership
https://www.forbes.com/2004/04/13/cz_kb_0413match.html
One of the biggest knocks against soccer is the lack of success of its professional leagues in the U.S. The latest to make a go of it, Major League Soccer, has lost $350 million over its first eight years. But when you look at the number of people playing soccer, its a major growth sport. Almost 18 million people played soccer in 2002, up 15% from 15 years ago according to SGMA International. Baseball participation is down 31% over the same period to 10 million people.
On a global scale, soccer leaves baseball even further behind. Soccers preeminent event, the World Cup, which takes place every 4 years, had 1.1 billion people tune in to watch the final game in 2002 between Germany and Brazil. The tournament had a cumulative television audience of 29 billion people in a total of 213 countries for the 64 matches. Baseballs biggest event, the World Series, is a non-event outside of North America and Japan. Viewership in the U.S. for last years World Series averaged 20 million per game and ratings were down more than 50% from 20 years ago
In the US MLS now equals MLB among teenagers.
http://www.espnfc.us/major-league-soccer/story/1740529/mls-catches-mlb-in-popularity-with-kids-says-espn-poll
In this worldwide survey Baseball ranks 11th.
http://www.totalsportek.com/most-popular-sports/
The NFL has ranked more popular than MLB since 1985
http://www.espn.com/nfl/story/_/id/10354114/harris-poll-nfl-most-popular-mlb-2nd
I haven't seen any world wide comparisons but baseball probably doesn't get as many spectators as its cousin Cricket where test matches in Australia, India and England have spectators in the hundreds of thousands
http://stats.espncricinfo.com/ci/content/records/283309.html