Would a Reraise ability break the game?

[Rongway]

Yeah but this is exactly the scenario that would have to be avoided. Imagine cheesing big mechanics like this.

There isn't much cheese to be had. For the game's more difficult fights, if a healer has to LB3 the group wont beat the enrage window. For all other fights, no one cares.

You underestimate folks. Remember that healer LB3 doesn't give weakness, and most groups can generally clear without using DPS LB3 outside of week 1 or 2. This could potentially affect older ultimates as well where damage doesn't matter any more only that people do mechanics correctly.

off the top of my head, a good example of a mechanic that would be super easily cheesed was Lions in E12S, people already cheesed it with Heal LB 3 because parties messed it up all the time, the issue was the healer had to get lucky and live but a reraise would basically make it a standard strat.

And dmg checks were definitely met despite this.

Yes, I agree.

On the other hand healer LB3s and Tank LB3 have been used to cheese a lot of things already, so this isnt like mind blowingly broken but it does make it more accessible. Just as an example this whole tier tanks have been cheesing Cachexia 2

The difference I see, at least in more recent raids, is if you tank LB a mechanic the whole party can still get a major Damage Down if the mechanic isn't handled correctly anyway. With a Reraise+wipe+LB3 everyone loses gauge and a few GCDs but otherwise comes back up with no Weakness (except the Reraised healer) and no Damage Down (except the surviving tank), which could tip Reraise into OP territory.