Nascent Flash was added in Shadowbringers because WAR mains were complaining about Cover having situational advantages in fights throughout Stormblood. They complained about DV/PoA as well, which was why SiO was reworked into a completely new action mid-expansion. I think that was the first time in this game's history that the devs threw out a newly added action and replaced it with a new one simply because a job's players demanded something more powerful.