I agree that jobs should be interesting and be able to interact with eachother, because if your job can uniquely influence the party and you can only choose one of multiple abilities to use, then it makes the overall battle different each time.
What used to be a lot of fun, for example, was how Bards could increase MP of the party, and this allowed Paladins to spam Holy Spirit (which they quickly nerfed). Mana Shift was used frequently to help rezzers, because MP actually mattered more due to having less off-global heals.
However, I don't think just replicating Heavensward is the way to go. There were genuine problems then that they were trying to improve with the changes they made:So rather than just copying Heavensward, things like this would need to actually be implemented better overall, such as:
- A lot of abilities were bloat or such rarely used attacks that it was pointless.
- A lot of abilities were flat out unused, pointless or sub-optimal.
- A lot of stats were pointless or annoying, such as Parry (RNG physical mit that didn't consistently help with the primary tank threat of tank busters), Accuracy (effectively gatekeeping raids too much because you'd miss attacks if you did it wrong), Elemental defenses (since each enemy uses different elements for each attack, it would be pointless and not realistic to switch for each boss).
- Rotations were hard for new players to understand and rarely executed correctly, leading to a fraction of the damage they should be dealing on certain jobs. The jobs just weren't intuitive at all and had no tutorial, and the game is often played by partners of gamers who aren't that great at gaming.
- Status effects are something MMO players are used to, but many join FFXIV as their first MMORPG, so changing that to Job Gauges made sense but it also trivialized things a bit by making them feel more similar (get gauge to 100, spend) and usually having no time limit.
- Make every ability useful and have purpose. And don't add damage to utility, otherwise we won't use it as utility ie. gap closers. They currently have purpose, but that purpose is mostly damage now, or not very unique.
- Keep Tenacity as a sub-optimal damage stat but make tanks want to consider it more by having very hard-hitting auto-attacks.
- Add elemental stats again and make them useful by having players cast an elemental buff on the party. For example, if a dragon is going to cast fire attacks, a Black Mage could cast fire resistance on the party. White Mages could cast earth offense on the party if an enemy is weak to earth, or wind defense on the party to protect from Wind Sprites. And if the party doesn't do these things, incoming damage should be extremely high and outgoing damage should be extremely low. A lazier way that they've already done could just be an elemental wheel, but it means no party interaction which is what we need more of.
- Make MP more likely to run out again, such as by having ability heals consume MP. Speaking of which, make healers actually have to heal in the first place which has eroded in higher level dungeons. All this will lend itself to bringing MP share abilities like Mana Shift and Bard's MP regen back.
- Having Skill Trees will help story-only players, non-gamer partners and journalists to play by having the default Skill Tree build be really easy and hard to get wrong, while others can be more sophisticated with greater control of party utility, buffs, debuffs or a bit higher damage potential.
- Tutorials on the first use of each action or scenario. FF16 does this so they know how to do it. FF14 actually does it with Active Help, but it's not job-specific.