I'm not seeing playing in firstperson mode as a disadvantage so far - there is the odd person obviously using hacks but that is another story.
The game has "hidden" effects of recoil/spread anyhow - if you burst fire you'll still do better usually even though it looks like your rounds are still on target.
https://forums.battlefront.starwars.ea.com/discussion/6989/first-person-vs-third-person
Reading atm not looking good.
The BIGGEST advantage is being able to peek around corners while in Third Person. It is even a bigger advantage in the smaller objective modes when you are trying to defend. Another big advantage (like someone else said) is that you don't notice the "flinch" as much. You also have a better idea of how well you're moving or strafing during a firefight (not enough people do this! This isn't Counter-Strike, don't be afraid to move while you are firing!)
The ONLY disadvantage is shooting or throwing your grenades into walls
Pretty much what i feared, So is there no HC mode then?