So the argument from Assange was that all relevant information from the cache was already public from previous publication. The entire cache was public when FP published the article you're referring to so they could have pointed out what was actually worth reporting if there was anything.
The point about the 2012 Syria emails is more interesting, but the whole point about Wikileaks running cover for Russia never made a lot of sense to me since they have published damaging info about Russia.
ETA: I'd be remiss not to mention that the discussion of Assange's biases is a red herring to the real problem which is the US's attempt to criminalize publication of state secrets.