For most of FFBEs lifespan, all the content the most difficult content was designed around damage units. They were all beatable if you had the top damage dealer units and corresponding TMRs. After the release of Orlandu, a further requirement was added that your damage units needed to be chaining. We then had a short meta where chain cappers and finishers became a thing with Olive and Firion. This is now a thing of the past.

Everything has changed since the release of Tilith, Rikku, Zarg, and 9s and the last two trials. The difficult content now is based on attrition. The fights are 30 minutes to several hour affairs that require multiple support units providing mana sustain, reraise capability, teamwide stat buffs, elemental resists, and ailment resists. Your damage units are basically an afterthought for challenging content. It is all about surviving sustain. If you can do that, then whatever damage unit you bring is fine.

The realistic cap on the amount of damage units you can bring is now 2. This results in chain cappers/finishers become useless. At this point, all of the damage based units are basically the same. It doesn't matter if it is Orlandu, Tidus, A2, Dark Veritas, etc. Whichever one you use, you just need to pair with another unit that has an attack which allows you to build a chain. There really isn't much difference in using one over the other. Occasionally they have a minor support ability or killer that helps in a specific fight, a few of the damage dealers do deal more damage than other, but that is the extent of the differences.

The situation with support/healing units is completely different. Units like Rikku, Tilith, and Zarg have virtually no substitutes. There a huge lack in the total amount of available support units and the current support units we rely on are not replaceable with other support unit types.

The only non damage role with meaningful unit selection is tanks. We have about 3 tanks that are currently usable for the highest difficulty content. For healing the only realistic option is now Tilith. Being realistic though, is healing even a role since the release of Rikku? IMO, her design was a flat out mistake. Every encounter from now on has to be designed around reraise. This makes all the future encounter design space more limited than it needs to be. The problem is furthered by the fact that there are no realistic substitutes for her.

If you are going to design encounters around needing a specific ability, then there needs to be more than 1-2 characters who have that ability. We need 3 characters that can do Rikkus or Tiliths job. We need a much larger pool of characters designed around support in general. When Ramza gets enhanced we are going to run into the same issue again where there are not enough units that can provide big party wide buffs.