https://www.reddit.com/r/hearthstone/comments/qmmb0x/hc_banehollow_mysterious_stranger_worth_it_to_do/
Rarran reported this in a stream back when he was doing Mercs.
The reddit post showed a stronger correlation for “number of fights” than for “node number”, which would argue that skipping fights to reach the node is a bad idea.
Ten months old, and blizzard has reported changes in Stranger rates since then.
I’m not aware of any reported data since the last patch. People who really care should collect and report their results.