NR have been wearing this phrase out since their Nuke Trump issue came out.
It's ironic that NR employs Jonah Goldberg, author of 'The Tyranny Of Cliches' and that Goldberg participated in the Nuke Trump issue (as well as a mountain of anti-Trump columns prior to...he's got a very large axe to grind), because 'diverse conservatives' is an oxymoron when we are talking about an agreed-upon set of principles.
When a group of writers engage in mob behavior diversity is rather thin on the ground.
In this regard, National Review is just like the liberal lamestream media.
Same behavior. Same mentality.