Yeah... the level steepness gets pretty high the last few places/battles in emerald. I have no idea how you are supposed to compete coming out of Gym 8 with possibly Lv 35~40 mons and going to the E4 which goes from Lv 46~58... At least in Emerald there is no BS Metagross that gets Meteor Mash attack boosts every time it uses it...Okay so when I made it to the Elite Four, all of my mons were below level 40, and I got absolutely manhandled.
Are you limited to GBA stuff? In which case you should try Mystery Dungeon Red Rescue team and see how that goes :P