Almost all of the cost controlled MLBers are Theo's acquisitions (Betts, Bogaerts, Bradley, Swihart, Vazquez, Shaw, Owens), as was the top prospect traded for Kimbrel (Margot). Ben gets credit for those because he was Theo's right hand man? So basically, Ben gets credit for every good move that occurred while he was in the organization, and all the bad moves he made was ownership's fault.
Also, in general, it's a lot easier building a farm system when the MLB team stinks. Higher draft picks (Benentindi) and the ability to trade impending free agents for prospects (ERod), rather than the pressure to trade prospects for another piece to a playoff push. Theo never had that luxury, while Ben had that advantage 75% of the seasons he was GM.