I have to agree that it all shouldn't translate into character as masteries, although beyond what's been stated here, one could go with the "Jack of All Trades" idea, and have a bit of proficiency in a lot of things BUT have no main specialty that is mastered. This gives you an IC reason for cycling between jobs a lot, but doesn't tread into Mary Sue territory because you either only know the basics to the class or are slightly proficient at it, which isn't over powering when done tastefully.
Also, if you go from one mastery to another, there's always the option of RPing learning that new mastery; this, however, takes time that a lot of players don't really consider. I don't think I'd balk at someone who took an entire year to RP out going from a master Archer to a master Conjurer, even less so if they took longer than that; I would, however, not buy that it only took a few months.
Just some additional food for thought!
Also, if you go from one mastery to another, there's always the option of RPing learning that new mastery; this, however, takes time that a lot of players don't really consider. I don't think I'd balk at someone who took an entire year to RP out going from a master Archer to a master Conjurer, even less so if they took longer than that; I would, however, not buy that it only took a few months.
Just some additional food for thought!