Champions are pushed out by the other medium based infantry. Both Tharn and Warmongers are very good against champions because they generally out threat them and have no real trouble with the high DEF.
I do not think the chamos are worse than ravagers/warmongers but when they fight each other, champs are worse. Champs are probably better against heavies though, so id say it os a meta thing.
In my experience they are indeed too slow and die too fast if they leave Madrak1's DEF bubble - which makes them very weak in SR18 live scenarios. And people don't seem to mind hitting DEF 16 in melee or 14 with guns. Sanguine bond only helps you so much..
I have a shaman in my Kolgrimma list currently, but he doesn't do much. I expected him to extend her cloud wall but he is often out of position to do so. It's the medium bases man
(on a sidenote) Did you by the way ever write some reports from your ATC games?