He's only like 5'7" now so it's not like they made him a giant. Giving growth hormones to kids with deficiency is, I think, standard medical practice now. I know a boy who got HGH and ended up like 5'6". It was done to prevent dwarfism and promote healthy development.
It wouldn't be an advantage to make him a giant - arguably it would be a negative due to his style. However, HGH allows substantially faster recover, and basically any athlete would take it if possible. Messi was able to do so legally unlike most footballers due to his condition.
