So I was thinking about what jobs could branch off of what classes without changing the main hand weapon and there was one that stuck out. I am not going to spoil the story of the game this class is in but in FFIV the after years one of the classes is the Holy Dragon Knight (HDK).
Its main job would be LNC its secondary would be GLD and its third would be CNJ. When the soul crystal is equip'ed the tanking stats would increase and the job abilities would focus on reducing damage and hindering the enemy (if you want to be true to how the class would work it would require some form of jumping ability) like a jump that reduces the overall damage for a period or grants a defense bonus to the user. But that's just my idea.