Initially The Y-Wing was the official Fighter/Bomber of the rebellion and even pirates Due to its "Survivability".... It can stand a lot of firepower thanks to its powerful shields.... The Y-wing Should match a Tie fighter.... thats my opinion
It has strong shields but lacks the maneuverability of most fighter craft. If the same concept from sins (fighters squads having more units than bomber squads), then I would think a group of Ties would be able to take on a group of Y-Wings and win. It's really hard to say, though, since the rebellion has a couple utility fighters, like the Y-Wing and the B-Wing that serve both a fighter and a bomber role. Especially B-Wings, since they should be equally effective against both fighters and ships.
If they scrap the whole "fighter or bomber" thing, and it was 7 Tie fighters vs. 7 Y wings, then I could see it going either way. If Y-Wings could use missiles against other fighters, it might actually be way in favor of the Y-Wings. I haven't seen anything about how the fighter system will be handled though.