I think Bungie will have to discuss how to address this use of synergy if it becomes more prevalent in PvP. In reviewing the stated and intended abilities of a Defender Titan, I see no exploit here, if by exploit we mean to use game mechanics in a way the developers did not intend. Bungie created the Defender to be able to generate and feed Orbs to a fire team. I think it's clear that this strategy presents something of a problem for the game as a whole, but I find it hard to believe that Bungie couldn't foresee this kind of scenario.