We can all agree that large scale balance is not good. It's generally accepted that the introduction of scourges and firebrands in PoF was the nail in the coffin for a combat system that was already beginning to break down in HoT when people started to stack Condi revs and condi reapers. Since launch, the community has suggested various changes to curtail the dominance of firebrands and scourges, and a few of these were implemented by the developers. Unfortunately, here we are 1.5 years later and we are still talking more or less about the same problems we had since launch. Despite several consecutive patches nerfing the overall strength of scourges and firebrands, (Sc and FB) they alone will comprise of 85%+ of any seriously organized group.
I believe that the lack of significant progress is due to some fundamental misunderstandings of class dynamics. The problem is not necessarily the magnitude of FB and SC abilities, but rather the relative performance spread across a variety of roles that in HoT could only be fulfilled by one class. Said another way, the meta firebrand is basically the compression of base guardian, Healing tempest, boonshare mesmer, and boon revenant into 1 class. It may not outperform a specialist in each of these areas, but the fact that it can even compete with healing tempest, while out stabbing a core guard, outbooning a mes, out-resistance a rev and on top of that have AoE instant-res, reflections, mass condi removal and also be nigh immortal, is a problem. In summary, the problem is that FB is an alleged jack-of-all trades that can easily outperform specialist. A similar problem exists with the scourge. There is simply no substitute at all for these two classes in any interpretation of the meta.
Say for instance we decide that Firebrand healing is too strong and we decide to completely gut it's healing coefficients. Since we still need consistent stab, condi removal and boons, the firebrand meta will remain in place, and nobody will even consider trying to replace the FB with another class because your comp would then be deficient in at least 2 other major roles. What about buffing other class? We can give massive buffs to tempest healer, but nobody will ever slot them in place of a firebrand because they still cannot compete in other areas such as boon coverage, condi removal, and stab and so overall their a poor substitute. So instead the super-buffed tempest will compete in the remaining 15% of the squad space which means that they are going to be pushing the other outcasted professions like the healing druid, and tablet rev. In summary, the problem is versatility and the overall spread of performance across many roles. So long as the firebrand can reasonably satisfy 2 or more roles, they will always be preferred over the traditional pre-pof classes.
I think the developers have two choices. The first choice is to scale up the versatility of other healers such as tempest, druids and revenants by giving them meaningful ways to simultaneously give stab, more boons (or at least unique buffs like auras), and remove conditions. This way they can realistically compete with the firebrand and commanders can assess the relative advantages of employing each class. If you played GW1 you would be pretty familiar with this concept. If you want massive damage reduction you had a lot of options: Imbagon, Soul Twister, or EMO. All of them could excel at the role, it just came down to tastes and what the player was most comfortable with.
The second choice would be to basically have unprecedented nerfs to the FB tome mechanics that would essentially strip them down to performing 1 or 2 roles. In theory maybe it could work, except that we still need stability (honestly the sheer importance of stability and lack of democratization among classes to access it may be equally perilous as this post), so we would still probably run it anyway. In general I don't really like this approach because if we gutted the FB without lowering everybody's damage we would probably turn into glasswars 2. Another problem is that it really doesn't guarantee any diversity because the other classes also have glaring problems in their design.