Why write a completely original or unique novel because the ideas you are really passionate about have already been developed?
Well, you shouldn't. You should write whatever you want.
I have original ideas but I also like to draw from mythology and my experiences. My stories come from my thoughts and my thoughts can only be mine, and so you will always find things about my stories that you might not have read before but I say 'might not' because (sadly) we can't read every book in the world and so it is entirely possible for another writer to have had similar ideas to mine and this means you will find familiar themes/characters/plots in every book you read, that doesn't mean I shouldn't write about them though, right?
My favourite authors have a huge impact on what I like to write. I read their books because I love their ideas and writing style and so my stories will naturally take a similar tone. I love fantasy, dystopian, horror and sci-fi and that is reflected in what I write. Should I not write what I want because others have written about these themes before me?
I hear things like "not ground-breakingly original" Well, is anything that original these days? Most bestsellers aren't totally original. How could they be? Should Suzanne Collins not have written 'The Hunger Games' because it was almost identical to Battle Royale? No way! How about Harry Potter? 'The Worst Witch' was the same theme, what if someone had told J K Rowling, 'Nah, we already have books like that out there, we don't need this one as well.
The idea that Harry Potter might not have existed is just ...
Having said that, writers must always be mindful about plagiarism. It's clear when a story has been copied almost word for word and that's not cool. What also isn't cool, is writers being afraid to write what they love for fear of the critics. YA and children's book critics often annoy me because they say things like "It's been done before." Yes, it might have but the children and young adults reading it haven't been that age before and they may not have read books created in 1965! They want something new, something written by a writer who isn't dead, something written for their generation and their generation only! Why should they have to put up with our cast offs? They should be given a choice of classics and new reading material. Language and technology and morality is ever changing and with new readers comes new challenges and new ideas or the best old ideas with a new twist.
Readers call the shots and I just hope they will fall in love with my worlds and enjoy wandering through them and being a part of them as much as I do. So, writers, write what you love and readers, read what you love. Don't settle for anything less.