General Shi has already been enfeoffed as a Prince; very few outsiders are granted the title of Prince by blood, and Prince Jing is an exception.
Because he was originally a Prince by birth. His aiding Zhao Xu meant he gave up his own princely status, far too great a sacrifice; giving him a new title of enfeoffment—no one would find that inappropriate.
But after conferring a princely title on General Shi, to then grant him a Red Book Iron Certificate as well—that was putting General Shi on too high a pedestal.
General Shi's merits are not small, but merits of this level, once a princely title has been granted, are not enough to warrant another reward of a Red Book Iron Certificate; otherwise the rewards given to the other generals would seem far too slight.
Conferring only the title of Duke on Prime Minister Zhao was precisely to keep the other generals' hearts in balance.
