Zac Gallen
The other name that Cardinals fans know all too well from the Marcell Ozuna trade, Gallen was an afterthought to move fans in the deal initially, ranking as the Cardinals' 24th prospect at the time and never appearing in a Major League game for St. Louis.
Gallen was excellent during his rookie campaign, posting a 2.81 ERA for the Marlins and Diamondbacks, as he was traded during the year for Jazz Chisholm Jr. He then finished 9th in Cy Young voting in the shortened 2020 season, had a down year in 2021, but rebounded in a huge way the last two seasons.
While Alcantara finished as the Cy Young winner in 2022, Gallen finished 5th after posting a 2.54 ERA in 184 innings of work and was once again an All-Star with year with a 3.37 ERA in 149.2 innings.
It is fair to wonder though if either starter would have reached their potential with the Cardinals. Gallen specifically has been critical of how the Cardinals handled player development, and we've seen position players like Randy Arozarena and Adolis Garica go on to perform elsewhere as well.