He is closer to a truth than you think. The better way to think about these groupings is traditions with a central dogmatic tendency. Eastern (theosis), Lutheran (Justification), Reformed (Sovereignty), Roman (Papacy), Baptist (Free Will). Lots of space within as long as you don't break with the central dogma. Where his truth breaks is that the mainline is a new tradition whose central dogma is there is no dogma that is true. Machen was right. It really isn't Christian. All the others can say the Nicene Creed honestly. I've never met a mainline cleric who can say it without redefining all the words. The 1920's-30's versions were at least like Spong and honest.