The devs don’t base Champion XP awards on the difficulty of the fight. Rather, they base it on the whether the activity in question is unlimited in activity for free or not.
– Challenge XP gets 2 per match because those matches are never repeatable, once cleared.
– Events that require sigils (Weekly Events/Dungeons/Delves/etc.) to run get 2 per match because they are limited in number, by either free and/or paid sigils purchases.
– Explores do NOT get 2 per match because they can be run infinitely for free.
– PvP modes get 2 per match… but those modes haven’t been revamped yet. I’d put the 2 per match in PvP on the endangered species list, personally. I’m looking right at you, 4.7 or 5.0.
The devs have said on a Q/A stream that of all the newer-style events, the Class events are the worst performing of them all. Slowly, but surely, the devs are correcting their design error. They want to push players to buy Champion XP from the Thursday event shop every week. They aren’t going to achieve that goal, if players are still allowed to farm Champion XP at reasonable rates infinitely for free.