I saw your earlier comment about the tail as well. I apologize if my comment came off as rude or short, wasn't intended to be! Basically Wrenthrush is structurally more like a Tapaculo to me. Not just the tail but it has a more rotund build and smaller wings.
There are plenty of plumage differences as well but I do see what you mean about the first impression. Honestly, though, I've never seen Wrenthrush in such good light to make heads or tails of the colors. It's kind of like trying to see flank color on Tapaculos - 90% of observations are a really dark silhouette
To me the most obvious coloration differences for Wrenthrush would be lack of the black eye line, darker/drabber color, and black feet...