You're right and I should clarify what I mean. Anton is very good at what he does; he has great technique. What he lacks is abstraction: reflection on his skill and an appreciation of the broader context in which it fits. He's astonishingly good at making friends and finding compromises that leave people not feeling too hard done by, but he's fundamentally so wholly practical that he can't really apply it elsewhere, and he's kind of reliant on people to protect him from actual malicious manipulation because what he does only works as long as everyone is fundamentally dealing in good faith.
Contrast this to van Hal or Belgar, who have pre-existing skills and biases, but the mental flexibility to view what they do from a number of different angles, change their mind about things, and correct us when they see us falling into a mistake relative to their areas of expertise. Anton isn't an abstract thinker and we never see him do that sort of thing, and I think that's what we need in a partner.