Imo the gorosei have mid tier physicals with top tier fruits. They’re difficult to fight but wouldn’t be a problem for a yonko or admiral to kill
I'm also thinking along those lines. If their regeneration is linked to their endurance, it indeed makes them just another Marco in life, capable only of delaying others. Being old, their endurance is carried by the Zoan they possess, which makes sense, to be honest. More specifically, I don't think their Zoan forms alone would be enough to boost their endurance to a higher level. That's why Oda awakened the Devil Fruits of the Goroseis, to further increase their endurance: old age resistance + endurance gained from awakened Devil Fruits + powers that only serve to delay.
I still hope that Saturn surprises me and starts using Adcoc-Haki in these physical attacks he's employing. So far, even though these rays are everywhere when he appears, we don't see any Adcoc-Haki leaking from his physical attacks...
If one of the closest men to Imu-sama is showing such poor performance here, it reflects that he might not be very powerful.