I wouldn't file the following under mistakes but rather "missed opportunities" or "thematic inconsistencies".

Gunner's description : For the Gunner, the output of a vehicle or ship weapon is the ultimate expression of projected power… He also sees his role as being a defender of all who ride with him in whatever vehicle he is crewing.

Yet, most of his talents don't work with vehicle weapons.

Also from the Gunner's description: Gunners are often faced with terrifying odds or unknown threats requiring nerves of steel and when their positions are overrun, hand to hand fighting is often the only choice they have .

Nerves of steel = Discipline as a class skill. Check. Not sure why hand to hand is mentioned as the gunner doesn't have brawl as a class skill.

The Saboteur specialization doesn't have access to the Bad Motivator talent. Seemed like a good fit.

The Infiltrator seems a little too combat oriented. I can't help to think it could have benefited from a few non combat talents such as Bypass Security or Convincing Demeanor.