Giannis may have showed some dominance lately but the King is clearly better than him as he is the best in the business.
Lebron is 34 years old now and have proven himself many times, his first appearance in the NBA finals was year 2007 against the SAS spurs, and although they got swept during that time but reaching the NBA finals is already a great achievement at a young age.
Using my calculator, (2019 - 2007 = 12 years ago and Lebron is 34 so minus 12 = 22 years old, that's how young he is.
I hope my calculation is correct, please feel free to correct me if I misstated some facts.