Both Taillon and Keller are former top prospects who have battle adversity during their MLB time. However, their adversity has been much different. One pitcher has dealt with adversity due to injury and one due to poor performance.
In his MLB career Taillon has pitched 466.0 innings in 82 starts. He owns a 3.67 ERA, 3.55 FIP, 6.0% walk rate, 21.5% strikeout rate, and a 0.93 HR/9. He also led the National League in complete games (2) during the 2018 season.
All of that said, Taillon has battled injuries throughout his career. His MLB debut appeared set to happen in 2015, however, due to Tommy John surgery it was pushed back to 2016. During the 2018 season he missed time due to testicular cancer and he missed all of 2020, after making just seven starts in 2019, due to his seocnd Tommy John surgery. If Taillon is healthy, he can be one of the top starters in the NL.
As for Keller, while he has been healthy, minus a short injured lsit stint in 2020, he has struggled as a MLB starting pitcher. The past two season Keller has made 16 starts for the Pittsburgh Pirates pitching 69.2 innings.
Keller owns a lifetime 5.81 ERA, 4.30 FIP, 10.8% walk rate, 25.8% strikeout rate, and a home run rate of 1.29 HR/9. Outside of his strikeout rate, none of these results are what you want to see from a potential top of the rotation starting pitcher. Regardless, Keller is a lock to start the 2021 season in the Pirate starting rotation.