"a key tenet" is correct and usable in written English.
It is used to refer to an important principle, belief, or idea. For example, "Respect for human rights is a key tenet of our company's culture."
A key tenet of holacracy is explicitness.
But the idea of scrapping a key tenet of Britain's fertilisation laws dismays many.
A key tenet of the Reggio Emilia approach is that art helps children express their thoughts.
The stress on pluralism is a key tenet of a modern libertarian socialism.
Obama observed that trust is a key tenet of a functioning democracy.
The slip-up violated a key tenet of the campaign: to avoid discussions focused on race.
Berry said a key tenet of the ENO was making it an affordable night out.
His need to clarify that his family wasn't plotting against Brezhnev points to a key tenet of the Prokhorovs.
These discourses paved the way for land-use separation to become a key tenet of 20th-century US municipal regulation.
BBC director general Tony Hall has made improving diversity a key tenet of his time at the BBC.
They will prove a key tenet of Africapitalism: that it is both necessary and possible for entrepreneurs and society to prosper simultaneously.
