How can the Volcker Rule limit the strategies of small banks and benefit large banks with market power?

Contrary to popular insight, the Volcker Rule can limit the strategies of small and less powerful banks more than those of large and powerful ones such as SIFIs (Systematically Important Financial Institutions). Thus, the Volcker Rule can be perceived as unfair to the public, making the performance of banks further polarized and eventually fail, despite its potential merits. Managers in small banks may need to be concerned with the Volcker Rule more than those in larger banks. For large banks, the smaller the size of their main sector, the more they diversify into speculative sectors. When the size of the main sector is moderate, we observe an inverted-U shape relationship between market power and the incentive for large banks to specialize in main sector. When the main sector is very profitable, the greater market power large banks have, and the more they diversify into speculative sectors. For small banks, the greater market power they have, or the larger the size of the main sector becomes, the less they diversify. These findings suggest large ramifications about the effectiveness and implementation process about the Rule.