The Panther had a high-velocity long-barreled 75mm gun, not an 88. One of the reasons for the development of the Jagdpanther was to put an 88 in the Panther chassis. The turret simply couldn’t accommodate the larger 88.
The Panther and Jagdpanzer 75mm KwK 42 gun was very good for the time. It was further developed by the French and used in their AMX-13 light tank for quite a few years after WWII.