(Bloomberg Opinion) — As one long-standing debate ended at Doha’s Lusail Iconic Stadium on Sunday night, another one began. Having led Argentina to triumph in the World Cup, Lionel Messi cemented his claim to being the greatest soccer player of all time. But on the field, his opposite number in the defeated French side, Kylian Mbappe, gave notice that he will be a contender for that title one day.