That is completely correct and the mindset that one should have while playing the game. As already said above it's not hard to get a "Assistant - Doctor, Engineer, Scientist" ID if you speak with someone from the department and ask him to teach you a little.
When it comes to security it's a little bit more complicated, that's true but I managed to convince several HoS's to hire from the crew and even if it's a traitor we are hirering, it would only spice up the round and make it more interesting.
Point is you can get people to teach you a job in every workfield if you speak with the people. Also a tip for the future, if there is no HoP the Captain is responsible for changing IDs and asigning people to new jobs, so make sure to poke him about it.