So here's some interesting stats.
Root: tests 53, 50s 27, 100s 11. Total +50 38. 100 conversion rate: 29%
Smith: tests 48, 50s 18, 100s 16. Total +50 34. 100 conversion rate 47%
Kohli: tests 53, 50s 14, 100s 15. Total + 50 29. 100 conversion rate 52%
Williamson: tests 56 50s 24, 100s 14. Total +50 38.100 conversion rate 37%
Root is a fine player but his inability to convert fifties to really big scores puts him well behind Smith and Kholi in the battle of the young brigade.