Now I don't see it how often talked about, but it has been a uncommon complaint how most jobs in this game usually just do the same amount of damage no matter the bosses and monsters involved when you're playing a synced instance or raiding and the overall damage from your group is always going to be same even if you're all playing at your best. Even having the current high end Gear provides just a minimum boost and nothing more. I mean the high end crafting gear seems to have more of a noticeable effect than the battle gear
Unless its POTD and HOH (that just kind of nullifies it all) or your a BLM (insert BLM memes here).
Also the over world monsters being largely weaker...and well nothing to write home about as any job can just curbstomp those.
So the question is why not give bosses and monsters weaknesses and resistances depending on the job being used to make all the jobs more interesting?
For a Flan for example its weak against Magical Ranged DPS via spells, but highly resistant to Melee and Ranged DPS.
Sure this "may create some inevitable issues" because people are bound to block others in PFs because they want certain jobs for raids mostly (which they already do to some extent).
In dungeon runs this shouldn't be a issue because you have the usual 3-4 bosses + mobs that will all have their resistances and weaknesses.
In a way it might get players to play other jobs so they can learn to be comfortable playing said jobs if needed.
Like for me I'm always playing Dragoon, but I found a boss was weak to Samurais and said party prefers a Samurai I could try to get out of my comfort zone to try it out.
That is just my 2 cents, during my time playing this game I really did notice that no matter the job that it will always be the same amount of time and damage no matter what you're fighting and that it seems it be Gear+PlayerSkill dependent more than anything else which to me isn't all that fun if there is no Job+bonus damage at play.
This isn't just my opinion, others expressed that most jobs in any given group roughly do the same amount of overall damage no matter what, emphasis on roughly as the numbers can slightly vary but not by very much.
One last thing on how would you solve the raiding aspect...well
I believe if certain jobs were given buffs that allowed lets say a Magical Ranged DPS gave a Melee DPS to bypass the Flan's resistance bonus, but only do normal damage that it will offer more dynamic and fun strategies in Roulettes, and raiding.
Maybe this isn't the kind of game for that, I know a long time ago there were Elemental Materia and that didn't work out. I just wish the jobs in the game were not all samey you know? Its the problem of the journey always being the same and it becomes less rewarding the more you do it over and over again.
I'm alittle bit all over the place with this text, but I hope I made sense.