Jose Fernandez was on his way to the Hall of Fame. Nobody his age had the degree of success he had in certain key categories.
Fernandez's career K-BB% of 23.8% is the greatest K-BB% for a starting pitcher age 24 or younger in the live ball era, which dates back to 1920. The bulk of that is built on his 31.2% strikeout rate, which is the best strikeout rate for starters of those ages, and there isn't a close second. Nobody else in that age group has a strikeout rate over 29%.
Fernandez wasn't just the best young pitcher ever at striking batters out, he was one of the best young pitchers ever at preventing runs and keeping batters off base. By ERA-, which adjusts for run scoring environment, Fernandez is the third best starter age 24 or under at preventing runs. His 67 ERA- is better than notables like Roger Clemens (71), Clayton Kershaw (72), Tom Seaver (72), and Bob Feller (73) in their age 24 and under seasons. His 1.05 WHIP is also third best for starters in that age group, and is better than Tom Seaver's WHIP of 1.07 in those seasons.
By FIP-, Fernandez is the greatest starting pitcher ever age 24 and under. His FIP- of 64 ranks better than anybody in the history of baseball, live ball or not, which dates back to 1871.
Fernandez was so incredible on the mound largely because of his fastball+breaking ball combination, which he used roughly 85% of the time. Fernandez was the best at playing his mid 90s fastball and crazy good curveball off each other. They both came from the same arm slot, and his curve broke so late that it looked like a fastball to hitters out of his hand before diving out of the zone. Fernandez also had a good change up that he threw to give himself a third weapon against lefties.
Losing Jose Fernandez is the most heartbreaking sports related death of my lifetime. The Marlins ought to just change "Marlins Park" to "Jose Fernandez Park" as a tribute not only to Jose's amazing life but the way he thoroughly dominated batters there. Fernandez's career in Marlins Park includes an incredible 1.47 ERA, .502 opponents OPS, 1.98 FIP, and 32.8% strikeout rate.