Since you are attending a T-10 LAC, I would definitely recommend that you finish your undergraduate here. In all honesty, I do not think that you can get a better undergraduate education at Oxbridge than you re getting a top-notch LAC in the USA. The way that you describe your interests also indicates that a LAC is likely a better place for you. LACs are really the best place to explore multiple interests, while Oxbridge really put emphasis on specialization. I also think that a LAC is by far the better place to expand creative writing skills
In general, based on your posts, I do not really see why you are looking to Oxbridge - everything you have written tells me “this person is a great fit for a LAC”.
BTW, I also think that you would do well in academia, either in English or creative writing, and I usually recommend that students avoid going to grad school in the Humanities.
So finish your undergraduate, and look to do grad school at Oxbridge, or likely anywhere you want - LACs are the best place for students who want to go on to do grad school.