Upscaled characters
SAB does not work like other events and instances, and if I recall it correctly it doesn’t give out any exp.
You do not play as your class in there; lvl, skills and traits do not matter. You get a pointy stick for main weapon and 3 hearts for HP (you can get upgrades later).
Astrid Strongheart, Norn Ranger.
“I wish juvenile wolves were bigger”
Super Adventure Box is literally a completely separate game – inside of Guild Wars 2. I even used a level 2 character (in addition to other characters) in it when I played it; there is no difference between you and anyone else.
However, you can gain more power within the SAB itself; things like extra hearts (health) by beating the first world, extra powers (like an elite skill), upgraded powers (upgrade current skills that you’ve collected to become better). All of it is only earned within SAB itself and the upgrades are permanent (and character bound, not account bound).
As Caveth said, SAB is 100% separate from the normal game. There are no levels, there is no experience, there are no item drops, nothing. Nothing is taken from the main game into SAB, and nothing is taken from SAB into the main game except for Baubles, which can be converted into Bauble Bubbles and used to purchase skins and a few other items, or rarely sellable skin drops from the chests at the end of each level.
Given that, you can enjoy SAB with any character and you will be 100% equal to everyone else (minus equipment and now upgrades which can be obtained in SAB and used only there). There’s no upscaling because everyone is level 1 in SAB much like how everyone is the same level in activities like Sanctum Sprint or Crab Toss. Don’t expect to be leveling your character via SAB though, besides Bauble Bubbles or rare skin drops everything you do in SAB is exclusively benefitting SAB only.