Thank you for a thoughtful response. Having no official theological expertise, I'll hazard the view that the Mainline churches implicitly accept the earliest councils,  but not the concept that conciliar views are sacrosanct. The triumph of the monarchical Papacy model within your own church has also put conciliarism in the shade and infallibility though rarely used has deeply wounded it.

 As to sola scriptura, it certainly once had great purchase even in the mainline churches, and remains the lodestar of faith. However, within the Mainline there are, in Lutheranism and Presbyterianism, confessional statements. Anglicans have scripture, tradition and reason, and the BCP. These adopt dogma long held within the church, and in the case of Luther a ringing defense of Real presence against Calvin and Zwingli who took a spiritual presence only view. Today, the evangelicals (an amorphous term) are closest to the sola scriptura model, and dismissive of fixed prayer and liturgy.