Your 51% graph posted above does not take into account the numerous individuals within those pools that make up those pools

Who are you referring to, the miners? Miners are no more involved in block production in Ethereum than stakeholders are in Steem and BitShares. The direct equivalent of Witnesses in Ethereum, those producing blocks, are the pool operators. Just like witnesses they can be multiple people in practice, but they function as a single entity. In practice there are more individual block producing entities in any given time frame in the DPOS blockchains than in any of the PoW or direct PoS blockchains.

As a result your prior statement is untrue, when measured empirically:

DPOS still reduces the overall number of points in the overall system that need to be coerced or corrupted to gain control of the network and/or cause harm to it.