I've held off commenting about Champions so I could think about it and see how it affected a couple of TR lives.
TL;DR Champions are nothing but (yet another) anti-zerging mechanism; they suck, get rid of them.
Look, Turbine, I get it: I've been a DM, I know what it's like to want your players to do things the way you expect them to; what I don't understand is why you seem to feel that way. A DM in a PnP game gets the thrill of suspense and gratification for having predicted what was going to happen, the feeling like they are always one step ahead, but you can't get that, so why this continual obsession over making sure that people run your quests the "right way?"
Yes, the complaints that start out, "I was mowing through an elite quest 3 levels above me, and I got killed!" are pretty silly, taken out of context; in context, these are 3rd+ life FotM builds in crazy overpowered gear that SHOULD be mowing through elite quests 3 levels above them. If they don't, what chance do 1st-life pure builds have? This essentially forces a split between new and veteran players, unless they (like me) are working through TR lives in classes that are currently at the bottom of the update totem pole.
Oh, and here's the most embarrassing part: Unless your intention was to make class balance even worse than it was after the Paladin/Bard supercharging, it hasn't worked.
I won't go into details, mostly because I have no desire to help you (Turbine) make this system more effective, but Champions are actually rather ridiculous; even in a stealth run, all they do is enforce a 2-second fight every 100 yards and waste SP on re-invis'ing. Again, unless you are playing a suboptimal build or class, like a melee monk or ranger.
And don't even get me started on the mysterious fragment rewards; you should have put exactly 1 additional inventory space in as an option, just to make the entire thing recursively pointless.