I haven't looked into who he's added and for what, but people shouldn't really be added to DT just for doing one or two trades with them. People who have done this in the past have been removed from DT and rightly so. I think the feedbacks that person has left for others should carry just as much weight as the deals they have done with that person. If a person has only really left a few feedbacks then they're largely useless in the grand scheme of the network.
That's exactly what the OP's numbers don't account for. Perhaps some sort of deeper analysis of downlevel trust feedback would help, e.g. how active the "subordinates" are. In any case, I disagree with the OP framing this as "manipulation" unless it can be proven that the DT1 member did it for reasons inconsistent with the purpose of the DT (murky, I know).