I also feel that a gimmick-based fight is not the right to go (also its one of the reason of "watch the vid or dont join"), but the problem is that otherwise it becomes hard to create a high difficulty for all the roles in "tank & spank" fight. Especially if u can just "lvl up" or "throw more bodies".

In pre-ffxii offline jrpgs one player was responsible for managing both healing, dpsing and sometimes tanking/mitigating dmg, also with multiple characters. If u transform it to a multiplayer game, the responisbilities become divided and not much is left for particular player.

One solution could be AI-driven fights instead of scripted. An enemy that wants to target healers/top dps more often, ignoring the tank. An enemy that when for example blm starts slow-casting long skill, he instantly puts a heavy hitting aoe under him. Or enemy that uses some standard pvp strategies against players like cc'ing healers.

Another could be having more unique gear attributes like giving additional skills, adding traits, changing traits, changing skills, enabling to cross class skills that u normally cant. Or serious elemental or attack-type resists. Then adding some enemies that are subject to "elemental wheel", do attacks that are mitigated by having certain resistance. This would add a "preparation" phase for encounter, but may prevent players that dont have the "optimal" gear (havent completed the "preparation") setup from finding a party.