Original ideas don't necessarily mean good ideas. Take my idea to combine a toaster with a toiler-paper dispenser - I think it's a fabulous idea to warm up my bog roll while simultaneously making a scrumptious snack. The Health and Safety board did not have the same opinion. People read books for any number of reasons; they're fans of literature, they enjoy compelling stories, they want to learn shit, etc. I've yet to meet a person whose sole/driving reason for reading is to find an original idea. Try not to get too caught up in creating something original, 'cause that's really not what people are looking for - most especially publishers, I'd imagine. And regardless of how original a story is, people will always find something to compare it to. That's just how people work. Try not to let it get to you if you can.
I've had the same problems at times, I'll explain something to someone and its all 'oh so it's like.... or oh that kinda happens in....blah blah blah. STFU mine is different lol! But the thing is most 'original' ideas have probably been done, repeated several hundred times and done one more just to rip the arse out of it . The way I see it, each writer will have their own view or spin on a idea or situation. That's the original part. So although your story may be similar in topic to 'Fantastic Beasts' it doesn't matter because your idea will be populated with different characters/sub-plots/environments and general story telling. That is how it will be original because its you telling the story in your own way.
