The "gainsaying of Korah" was intrusion into the priest's office ("no man taketh this honour unto himself," Heb. 5:4). It was an attempt to create a priestly order without the divine authority (Heb. 5:10). The modern analogue is Nicolaitanism (Rev. 2:6,15), the division of an equal brotherhood (Mt. 23:8) into "clergy" and "laity"; a vastly different thing from the due recognition of ministry gifts (I Cor. 12:4-31; Eph. 4:8,11,12), or of elders and deacons (I Tim. 3:1-13; Tit. 1:5-9).
---from the original liner notes of the 1909 Scofield KJV Bible
But I have often found it implied, not only in sermons (and of course one has no recourse to ask for clarification during a monologue) but in the attitudes of the church members. And I am pretty sure it has been and is being taught, and often, particularly in the believing Baptist churches.
These attitudes are the exact opposite of what believers are to understand from the history recorded in Numbers 16. Instead of supporting and apologizing for Nicolaitanism–which is another name for clericalism–believers ought to oppose it.
"No man takes the honour of the priesthood to himself" is an Old Covenant precept. It has no place in the New. Under the New Covenant all believers are priests. All believers have ministry gifts.
But what about church leaders? Certainly it is true that no man takes the honour of church leadership to himself. The question is, is the prevailing form of church leadership Biblical, or not? If it isn't, then the issue of taking the honour to oneself is irrelevant, superseded by a larger issue.
The New Testament is very clear that we are to obey those in authority. If you attend a church led by a clergyman, then I suppose you ought to obey him. Just remember, this is not the design of Jesus Christ for His church. He called the elders very clearly to the overseership in I Peter 5. And of these, the Word says, "Obey them that have the rule over you," Heb. 13:17.
Challenging the clergy system is not the NT equivalent of "the gainsaying of Korah. But the clergy system itself is its equivalent. Oh, that believers would accord to Jesus Christ a real rather than simply nominal Headship of His church.