It was hard to pick who I think will end up being the Pirates' best minor league rookie. Jun-Seok Shim definitely has the potential to be that, but because he'll likely not play a full season, that bumps him just below Thomas Harrington. Harrington is a right-hander who the Bucs selected in the first round with their competitive balance pick.
Selected out of Campbell University, Harrington put the finishing touches on an impressive 2022 campaign that saw him work to a 2.53 ERA, 0.94 WHIP, and 6.17 K:BB ratio through 92.2 innings. He struck out 30% of the batters he faced with a minute 4.9% walk rate. Both pale in comparison to him allowing just a single home run for a 0.10 HR/9 rate.
Many evaluators believe that Harrington is the high-floor/low-ceiling type of prospect. He only sits in the low-90s and relies on a slider, changeup, and curveball. However, his ability to spin his fastball helps it ride through the zone. His changeup is a plus-plus pitch, and his slider also sits at an above-average level. His curveball is the worst of the bunch, but it's still not a terrible pitch, and he can certainly use it effectively.
There are a few other factors that may help him in the long run and help him play beyond his prospect profile. He currently stands at 6'2", 185 pounds, giving him some projection to work with. He also has plus command, which helps his stuff play up. Another factor is his good athleticism he shows on the mound.