The reason job roles are so strict is to maintain relative desirability for all the jobs. Start moving into 'hybrids' and balancing issues arise and psychopathic elitists like residents here demanding you drop job X because it sucks on the spreadsheets.
This is supposed to be a casual game and that my friends is the road to ending this casual game and turning it into an FFXI shitfest. WHY ARENT YOU PLAYING JOB Y, ITS IDEAL.