Some quick notes on the new Advantage and associated reworks:
Advantage was indeed changed partially because it was just overwhelmingly effective once defense was a big factor in survivability--it felt silly putting all this effort into re-tuning the game to be less explosive if a high-burst character with old Advantage could crit and still 80~100% kill someone in one shot. The new Advantage was decided on because it had a big upside--while it's now harder to stack with other damage increases, it can act as an enabler for lots of on-crit mechanics. You can see this firsthand in several of the First Order character ability reworks, as they can now trigger many of their effects on a regular crit, independent of Advantage.
Advantage will cause AoE attacks to automatically crit every target hit.
Advantage will cause multi-hit moves (e.g. Rey's Flurry of Blows, Magmatrooper's Line of Fire) to crit each hit.
Advantage will not help extra attacks, as they are, well, separate attacks. (e.g. Dooku's Hindering Press)
Advantage is applied to the next damaging attack only. This means if you, say, use a healing/buffing ability that doesn't deal damage, it won't consume Advantage. It also won't be consumed if you're Stunned and lose your turn. This is why Advantage still specifies a duration--conceivably, if you stun-locked somebody long enough, Advantage would expire.
By the same token, Advantage will still be consumed if the target Evaded your attack--it only 'cares' whether you did a damaging attack, not whether that attack succeeded.
The only exceptions to 'next-attack-only' are Assists granted by Phasma's Fire at Will, which will refresh the Assisting ally's Advantage if they had it as soon as they finish the attack. This was a quality-of-life improvement to compensate for the fact that you don't get to decide who gets called for an Assist, which could cause you to expend Advantage undesirably, and that felt weird for the First Order leader.
The "once per enemy" thing on First Order TIE Pilot's Keen Eye means that you can't gain Advantage from a single enemy falling below 50%, healing above 50%, and falling below it again; in general, this means that in PvP and Galactic War, Keen Eye will "only" grant Advantage 5 times per battle. "Only".
First Order TIE Pilot's triple attack bug is actually definitely finally fixed as part of the reworks. (Probably.)
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