Bosses SHOULD have immunities and high resistances to certain spell types, while basic mobs can still be effected. This is the case in every final fantasy bar a few select moves like The End and Zanmato.
So you are saying bosses should be immune to the spells that would define that job? Also a lot of people don't consider FF tactics apart of the mains franchise/ they don't know or don't care about them all together. That is the reason why that person said 2-3 games out of the 13.