That's more Tony's insecurities, narcissism and leadership failures more than anything. He felt more secure to put "family" into top-tier positions, because he viewed that as less of a threat on his position. He would rather sacrifice the long-term stability and power of the DiMeo family to feed his ego. For example, Ralphie would have been a suitable senior leader, given his earning power, business acumen and ruthlessness. Tony would have been better off taking Ralph's success and multiplying it across the family rather than marginalizing and humiliating Ralph at any opportunity.

He'd rather have yes-men and suck ups around him than have someone call him on his shit (look at the argument Tony and Silvio had at the end of Season 5 about this).