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).
Tony himself admits his failings to Melfi in "Unidentified Black Males" during Season 5. She extracts from him the truth about why Tony S. wasn't there when Tony B. was arrested. In a rare moment of candor, Tony S. admits favoring his cousin and being a weak leader at times.
I would agree in part about Tony elevating Ralph. But Ralph was such a prick that he made it much more difficult to be promoted than necessary. Let's face it - had Gigi not died on the toilet, Ralph may not have ever been raised to the level of captain by Tony. It was only after there was literally no other logical choice that Tony capitulated.
