I just faced a speed fighter squad in Arena.
EDIT: The squad was 2k power below most of the others at the same rank, so I guess he did something right.
Their setup seems to be build around Poe Dameron and his Expose ability.
There was neither a tank nor healer on the team, which makes sense. If the battle is over quickly, you need neither of them.
(Technically, there was Old Daka as a healer, but she doesn't really heal actively when controlled by AI as far as I can tell).
Interesting concept, as you cannot use tanks against this setup: An all-attackers team with Expose, Stun and so on will take any tank down very quickly.
I guess a squad with three or more healers could be a good counter to that, as most attackers are not made for longer fights. And without a healer they will have a hard time when they go on cooldown. Adding to that perhaps a character that removed negative status from allies?