If we have 2-3 Holy Clowns stronger than Sakazuki/Admirals how would you feel about that ?
This would tear the fabric of the manga's entire worldbuilding as we know it.
MarineHQ + Warlords = 4 yonko
The government is satisfied with this balance as Warlords clean up the Grandline while Yonko take care of Rookies in the New World
The Marines oversee the world as a whole and fix any problems that counter this balance.
However, if it was in their hands, they would wish to put a stop to the pirate era. This is ofcourse a nearly impossible task when you have a bunch of strong pirates each locked up and fortified in their island, and attacking one will leave you open to other potential enemies like the Revos or a Yonko crew with their accompanying fleets.
But still, the WG is more than satisfied with how this balance works.
Enter Holy Knights, 2-4 PK level top tiers wiping the butthole of St. Charlos in Mariejois, spending their hours trying to find out who stole his ice cream, that are capable of completely annihilating the Great Pirate Era alongside the Marines.
No thanks lmao