The problem isn't with the concept of agency accounts, but with the 'empty' ones being flooded in the market. Many sellers offer fresh MCC-linked accounts with zero spend and no history, calling them 'agency.' In reality, they get banned just as fast as personal accounts in grey niches.
The real power comes from agency accounts with an active Credit Line. They have a higher trust ceiling because Google has already extended a line of credit to that business entity. If you're running gambling without that extra layer of trust (or at least a massive spending history), you're just paying a premium for a label that doesn't protect you