That would involve picking a spot on a very cluttered surface from rather far out and diving in. Flying along the surface of the Death Star, with all those towers seems kind of counter-indicated, when you only have the trench defenses to worry about in the trench. And Vadar & co were destroying them outside too. Only about 6-7 guys died in the trench, and when added to the 3 who escaped from the whole battle, you have to assume that the majority of the rebel fighters bought it on the outside. Look at it this way - all known surviors were guys who went INTO the trench! The trench was the safest place to be! Luke & Wedge were in there, and since that third survivor was a Y-wing (numerous video games confirm it is a surface-attack fighter), it would have been in the trench, too. Maybe most of the guys in the trench died, but EVERYONE who stayed out of it did too.