The "home every night for dinner" thing is annoying but necessary for the way I play - if they were away for long periods of time they would miss too much of their family's lives. Most of my sims get a year old every two days - if a parent was only home at weekends they'd be away from their kids for 2.5 years!

As for the career progression, I imagine that they have different job titles depending on where the sim is going with that career. A sim who is heading for the top of the Science career for example would be a PhD student for the first few levels ("Field Researcher" is them doing all their experiments etc.) and "Science Teacher" is them teaching at a university either at the end of their PhD or as a post-doc, depending on how long they've taken to get promoted. Then all the titles from there are just creative ways to describe their work at a university or research institution of some kind. Whereas a sim who is only aiming to be a high-school Science Teacher is working as a Lab Assistant part time while studying for a Masters in school teaching and "Field Researcher" is a substitute science teacher who also works at a science museum/ outdoor activity place while trying to get a school job. Then a sim who just took the first job that came up to earn some money really is a Test Subject - and if they are competent and organised and the lab is seriously short of people they might get offered an actual role as a very junior lab assistant who does all the admin for the human test subjects and/or some data entry.