Anything that limits the ways we can design fights would be a huge misstep, in my opinion. I hope that isn’t the idea.
Furthermore, I feel that limiting content to only be beaten by a specific party composition would also be a disservice to the game (in this case needing 2 WAR to do a specific raid boss fight because they can tank swap).
Ideally, we should design jobs of the same role to be complimentary to each other in ways that your optimal party comp would be to have one of each in situations that require more than one player of any single role. Still beatable by having more than one of the same, but giving an edge to job diversity within the same role type in a party comp.
One way to implement PLD tank swap could be to use your self buffing libram to empower lightning strike to not only build enmity, but to also put you on top of the aggro table regardless of the gap in enmity. Essentially this would turn your lightning strike into how the WAR horn currently works, if you were to use the self buff libram right before.
The one problem with this is that currently the cleanest way to do tank swaps in Orbus is to stun, then blow the horn. As a PLD you would have to throw your hammer, use your self buff libram after it hits, then lightning strike. In theory I like the level of coordination that would require, but I’m guessing it would get pretty messy in practice since the librams aren’t instant cast when you grab them.