At the time of this writing the Bucs are 12 and 14 under Don Kelly, and 24 and 40 overall. The bucs are also scoring more runs under Kelly.
The Bucs have scored 86 total runs under Kelly which is around 3.3 runs a game. The Bucs have scored 118 runs under Shelton which is around 3.1 runs a game. That is a slight improvement, but still bottom 5 in the league. I think the slight uptick is from the Pirates playing closer to their expected OBP and expected slugging because their real OBP and real slugging is around the same as under Shelton.
The unfortunate thing is that it is hard to see the Pirates improving this offense much. You don't want to move on from a lot of their current players. You want Davis and Bart to continue playing. Hayes will continue to play and so will IKF. Nick G is back and may help. I say may help because Adam Frazier has been hitting fairly well under Kelly. The Bucs should see big improvements at 1B with Horwitz playing there fulltime now. Reynolds under Kelly will be better than Reynolds under Shelton, though probably no fault of Shelton.
I don't know if Cruz will be much better, and Canario if he keeps hitting will be better than Pham and already is. I think Cutch's numbers will improve by the end of the season. So yeah there are some improvements to be had here, but all with the same players. Triolo and Pham are two that can be moved, but they aren't fulltime players anymore so their replacement will have minimal impact.
The best hitters in AAA right now are Yorke, Suwinski, and Solak. Solak was called up in May, but didn't play much so he can't be counted on to help the team. Suwinski is essentially now a fastball/changeup only hitter. He is whiffing way too much against the break even in AAA. Yorke has been playing better of late. His biggest weakness is the slider and he has been hitting it along with the 4-seam and curve. He isn't hitting the ball as hard, but his whiff rate has reduced. The Bucs may be trying to get him to improve his contact before calling him up. Yorke is the only hitter out of AAA who may improve the team this season.
The best active roster the Bucs may be able to mustar this season may be to call up Yorke and carry Davis, Endy, and Bart on the roster if Endy is healthy. These guys can replace Triolo and Pham, but again this will have minimal impact.