I can solo Champions (with a few exceptions, due to annoying skills) up to level 40-50 zones thanks to my two tanky pets. Most of the time the splendid chest rewards are crap anyways and not worth the effort.
some champion are really easy (slow and infrequent attacks that is easy to dodge with no mob). they just have a crap load of health.
i attempted to solo 2 champions before (because no one was around and i wanted to try). first one, i accidentally pull it too far and it runs back to it original spot and regen all its health after i got it down to halfway (and it takes a long time). so i got frustrated and just go in, open the chest, and get out, ignoring it completely.
the 2nd time the champion took over a village/outpost in an event. i got it down to 3/4 health. it used fear on me, it ran the other way, and regen health. i go at it again. got it down to 1/2 health. used fear on me and it ran the other way, regened full health again. then other people came.
i ****ing hate how easy it is for them to regen to full health.
so while i never successfully solo a champion, i can if i really wanted to (the easy ones anyway).