In Wonder Trade when you put a pokemon into it you get a pokemon around that level range. That doesn't mean you will get legendaries when you put in lv 100 pokemon, but a lv 60-100 pokemon. The range is huge because if it was lower it would take ages to get a trade.
Before anyone says it's not like Pokemon games, but in here we can encounter non-roaming legendaries.. Thats not like the game.