I understand what you're saying. You appreciate the thematic elements of the jobs, and the more "blended" they make jobs, the less opportunity they have to really explore the diversity available to them. e.g., a pseudo-bow/bard turns two potentially great and unique jobs into one. That's fine in theory, but sometimes the two jobs they mix aren't the ones you wanted. For example, I wanted a Mime in FFXI. Some people told me that BLU or PUP was the Mime--I already had my Mime. But it didn't have the thematic elements of a the Mime that I was looking for.
Some jobs can be, or need to be defined by this fusion of thematic elements. For example, a Black Mage, or Elementalist, in some games, would be broken down into mages of each element... water, fire, earth, etc. Some people love that--they want to specialize in a specific type of magic. But, when you combine all of these together with the character of the Black Mage, the result is something entirely different. Some people prefer this creation, while others wish they could part it out into something more suitable to their taste. The more you blend, the worse this phenomenon becomes. Class purity and definition are appreciated.
I think this way myself, actually, but I can tell you from experience that parting out these themes isn't always so easy when you're trying to obtain an optimal balance of coverage. It's not difficult to come up with 40 distinct classes, not even counting these thematic "special blends" like Dragoon, Red Mage, etc. that aren't as recognizable outside of the franchise. So if you know that you can't have that many, you have to resign yourself to some blending.
Personal anecdote: Edward is the only memorable Bard to me, and I always stuck him in the back row with a bow.