The BEST part about Champions so far has been the OMIGOSH factor when a swarm of them hit the party [obviously, this is likely not near as fun when playing with fewer people- or solo.]
That being said, the non-swarm prevalence of champions [There's usually at least 2 per group of mobs, in my runs] makes them rather too common for any meaningful impact.
So yes, decreasing spawn rate is the way to go.
And yes, insta-killing should be reduced.
But, unfortunately, those players I ran with who were saying "Finally, Elite [in any quest (rather than just specific ones)] is interesting again, and not just a yawn" will be disappointed- as will I.
There's an easy fix, though. I mean, really simple-
Make champions more poignant.
You can even keep most of them rather tame, as they all are now. Generic effects, like damage boosts. That'll make these spawns all the more potent:
Just add in a small chance for any of the following to be a possible boost on a champion:
1: 15% movement speed buff [25% if they're orange named]. 10% increased attack speed. This creates an AHH! SPEED-TYPE CHAMPION! moment.
2: Spawner (Essentially an Ooze Guard/Eidolons effect, but based on NOT attacking it (and cap of 6 spawns, 1 spawning every 10 seconds to cap), creating units of power of one difficulty level lower (IE, an Elite champion would spawn quest-relevant mobs of Hard CR)) This setup allows for a reason to focus on the champion- preventing it from being able to create mobs- but also doesn't severely penalize the players for not focusing on it, by way of not making the spawns as hard as other creatures in the quest, and thus a severe danger.
3: Aura. We've already asked for these.
4: Transformation: Much like heroic orchard, for champions in certain areas, give a chance for them to auto-raise once as spectral versions of themselves.
5: ..well, so forth.
Give us some REALLY JUICY moments, ones interesting enough to have to keep in mind- not just 'Oh, okay, this one is a black wolf, not a grey wolf, and thus has +5 DC on trip attempts.'
Though in honesty, champions aren't even to THAT level of interesting [per individual champion] yet, which is rather disappointing.
As is, champions are quite fun as a concept and an overall element, and I'm enjoying them-
But each champion individually lacks any meaningful impact at the moment, and reducing damage and spawn rate, while definitely necessary, is only going to drive that point so far down that champions'll just end up being 'that slightly bigger ogre we have to hit a few more times'- as they mostly are already, now.