M-W defines an archetype (n.) as "the original pattern or model of which all things of the same type are representations or copies".
When we look to the ever-helpful Wikipedia for guidance, we learn that Tolkein's beloved Gandalf is an archetypal figure himself, the wizard-as-advisor, of the likes Merlin — who himself was quite possibly modeled after religious authority types (like Odin).
Hold up, JRR Tolkein, the father of modern fantasy, was unoriginal? His main characters had been done before? His venerated series is allegory?
You may be wondering why the Hell I'm giving you a vocab lesson. The truth is, I think that we (writers, agents, etc.) can use the reminder. There is a big difference between the use of an archetype and a lack of originality.
The goal of a work of fiction, as far as I am concerned, is to pull something new and exciting out of those old stories and characters – out of the familiar. That balance of new and old is what makes a great story great, in part at least.
We've got to move past the anything-with-a-school-is-like-Harry-Potter and anything-with-a-butt-kicking-female-protagonist-is-a-Buffy-rip-off reactions. See stories for what they are, and if they're good enough, it won't matter how many tropes the author used.