For his Masters of Divinity degree, Eric Powers has written a thesis entitled "Is there any Biblical Warranty for the Doctrinal Triage," which can be accessed here. In this 2016 thesis, Powers argues that there is no biblical warrant for the doctrinal triage: the view that doctrines can be split into first-order, second-order, and third-order doctrines. Citing Al Mohler, among others, the triage is described as follows: first-order doctrines are those that are non-negotiable; second-order doctrines are those that are "denominational distinctives" and are doctrines that, while serious, Christians can disagree with without calling salvation into question; third-order doctrines are less serious doctrines that Christians can disagree on within a church (pp. 13-14). Powers engages some of the texts used to support this notion of doctrinal triage and shows that they do not in fact promote this teaching. Rather, any claim of order of doctrine is one of the relation of foundation to the building. In this view, the foundational doctrines are required for the other doctrines, yet there is no sense in which we can say that the doctrines built upon that foundation is any 'less important' or 'less essential' than the foundational doctrines required for them. Interestingly enough, Powers appealed to the unity (and simplicity) of God to ground his view that all doctrines are "relevant to the believer and are equally true" (p. 68; pp. 68-73).
Coming from a confessional perspective means that I do not start with a view of doctrinal importance based on some notion of triage. At the same time, the doctrinal triage is practiced in broad Evangelicalism, under various names, and it is clear that it has been used (or abused) to allow for toleration of doctrinal errors within the church. This thesis is indeed a helpful piece of work as it addresses the tendency within Evangelicalism to water down and downplay doctrinal differences among professing Christians and churches.